God is a conjecture; but I desire that your conjectures should not reach beyond your creative will. Could you create a god? Then do not speak to me of any gods. But you could well create the overman. --Nietzsche
Whenever I tell people I'm a staunch atheist, they automatically assume it's because of my scientific background; that I don't believe in a god because there's no proof of its existence. But that is a straw man and far from the truth, which is that I believe in many things for which there is no proof. I clearly acknowledge my belief in the non-existence of a god is just that: a belief--nothing more, nothing less. In fact, there was indeed a time when I believed in a god, until the age of seven. It was at that age when I decided to the question my beliefs, which ultimately led me to the conclusions below after years of refinement.
However, I do have reasons for not believing in a god, and, more strongly, I believe there is strong argument to not believe in the relevance of god's existence (even if god itself existed). In other words, I have chosen to deny the existence of a god, which is the definition of atheism, since I find god to be irrelevant.
Below I outline the objections I have against the concept of a god (a concept I believe that was created by man, as theorised by Nietzsche and others). I'm loosely defining the notion of a god to be an extremely powerful being who may or may not be responsible for the creation of the universe and who supposedly has the power and the ability to judge sentient beings such as humans. I also assume god is external from its creations (though this is not necessary except for cogency). In all these objection arguments, I begin by assuming that a god does exist, but I explain why I don't acknowledge its power, and consequently my belief in the irrelevance of its existence.
There's an old adage: power corrupts. It follows that absolute power corrupts absolutely. Of course, a god's power might not be absolute, but nonetheless how do we know a god is not a despot? In fact, almost every religion portrays god as despotic: "Do this, and you will face god's wrath." "Pledge your allegiance, plead forgiveness, and you will be saved." It's strange to me that a powerful being would want and need such statements from its creations and even resort to threats to make its creations comply. It is a sign that all the power has gone to its head and that we, god's creations, are no better than slaves. God is on a massive power trip because it has created a universe where the creatures have flaws in them, and then god delights in "punishing" these creatures for falling prey to these flaws and not begging for forgiveness.
Omnipotent or not, any god that chooses to "rule" over entities it has created reeks of despotism. I view such a god as no better than Hitler. I would never believe that such a despot is necessary or even worthwhile for my existence.
Some of the concepts here are illustrated in the song Oppression: the thought police are coming by my band TWISTED HELICES.
Following on through with the power corrupts objection, what gives god the authority (except for physical strength) to judge what is right and wrong for its creations? Who is god to say actions a, b, and c are wrong and should be punished and actions x, y, and z are good and should be rewarded?
Being a firm believer in relative ethics, I believe I know best for myself what is right or wrong, as long as I am consistent. My general philosophy is the conjunction of these two axioms: don't do anything to others you'd not want done to you, and do only things to others you want done to you. As long as I adhere to this philosophy I think I am the ultimate arbiter of my actions (I often say I am my own god). Even though a stronger force could "punish" me for doing something it doesn't like, there is no moral, ethical, or logical grounds for doing so.
So at this point, not only do I reject the idea of a god who is more powerful than me and therefore demands my obedience, but I also think that such a power (including my creation) does not guarantee it any superiority over me on a ethical level.
Some of the concepts here are illustrated in the song Morals are Arbitrary.
This follows from the morality objection. Believing that someone other than you can tell what is right or wrong for you encourages conformity and lack of responsibility for your own actions. Consider the concept of "forgiveness for one's sins", wherein every wrong is wiped out and you start with a clean slate the moment you accept/believe in some arbitrary god. How can this encourage personal responsibility for one's actions? How can this encourage thinking for oneself, figuring out the hard way whether something is right or wrong, instead of just doing what is spoon-fed?
This is why when Nietzsche said "god is dead", he wasn't leaping with joy but rather lamenting the fact. In other words, there was a time when the concept of a god might have been good to keep humanity in line, but today, since most people follow a double standard, it's easier to discard responsibility by using god as an excuse.
Some of the concepts here are illustrated in the song Let us Blame God.
Let's assume that god is indeed not despotic. If this were the case, such a god would at the very least be apathetic, allowing all the atrocities in the world to occur while not doing a thing to stop it (unless god gets a perverse pleasure from watching humans suffer, in which case such a god would be cruel). This in and of itself isn't a bad thing, but it would illustrate that the relevance of a god's existence to our lives is close to zero and there's no reason to believe in it.
This is similar to the morality objection but it works at a fundamental level, at the very fabric of what we call reality. This is the most generous explanation for the existence of a god that I can provide. In this explanation, god is neither apathetic nor despotic, but has created a universe which it has chosen to not control.
Even though our knowledge is incredibly miniscule and what we don't know is infinite, science has shown something conclusive: at the quantum level, the universe is non-deterministic/random. This is a conclusion that arises not from quantum theory, but from quantum fact, i.e., what we observe regarding the behaviour of quantum particles. In other words, even if a god exists, that god has created a universe where it has no deterministic control over. Einstein was one of the people who objected to this idea of a non-deterministic universe, claiming god does not play dice, even though he was one of the people who was responsible for a lot of the ideas that lead to this conclusion. But in the end, Einstein was wrong and god does play dice.
One objection to the above argument is that rules that apply to us don't apply to god, and/or that there could be an underlying deterministic reality that we do not have access to. For example, it could be argued that the universe is a great (computer) simulation where god is supplying the randomness to us from a pre-determined random sequence (determined, say, by some natural source of randomness in god's environment and stored on some fixed device). Even if this were the case, it still would indicate that god has no control over the numbers that show up. God would just know what the next number is, but not be able to influence the behaviour of a particle which is the function of the random number. If god did influence the behaviour by changing the random sequence to reflect its desired will, humans would not perceive it as random. Therefore, even if there's a underlying determininistic reality beneath the quantum world, determinism at the quantum level is not possible, even for god.
The quantum mechanics objection also could be stated as the free will objection, in that if you assume we have free will, then god has created a universe where it cannot control the behaviour of humans (keep in mind we don't need to assume quantum particles are non-deterministic in behaviour). Regardless of how one looks at it, the inescapable conclusion is that there's no reason to believe in the existence or relevance of such a "hands-off" god. It doesn't matter either way.
Many a time, when these types of objections are raised, believers in a god will say our minds are not capable of comprehending of an omnipotent or powerful god's actions; in other words, we're like ants trying to comprehend human actions. In this event, I'd argue that to a god, we're just like how ants are to a human. When ants come into our house, they could be praying to me all day, but the Orkin man still smites them randomly without caring about whether ants are good or bad. Which would explain why humans get "smited" all the time without rhyme or reason.
This is very simple: who or what created god?
Assuming a god existed, it really is very anthropocentric and a show of hubris to think that an all-powerful god created man so man could worship and praise god. In fact, this really points to a human insecurity. Humanity's existence may well be pointless and random, with bacteria being god's chosen organisms of interest, but most humans wouldn't be comfortable with that. Even more bluntly, the concept of a god wouldn't exist if humans didn't exist, so god is an anthropocentric creation of humans (conveniently made in our image).
The above point, turned around, leads to the question in general: if there is an all-powerful god, why would such a god need to create anything else? Amusement? Boredom? Insecurity? This would reflect a strange psyche on the part of god.
Finally, even though this is loosely connected to the notion of the existence of a god, I am also against religion in general, particularly organised religion. In many ways, science is as much a religion to me as any other, but the one fundamental difference is that I constantly question my beliefs and I try extremely hard to prove myself wrong (or ask others to do it for me) in a true Popperian spirit. Few religions permit this, and fewer would permit speaking against it and overturning it on its head.
Another reason I don't think much of religion and god is because some of the greatest atrocities in humanity's history have been committed in the name of religion and god. Religion has the same sort of problems I outline above: it encourages despotism, conformity, acts of barbaric cruelty, laziness, and lack of personal responsibility. Sure, religion and a belief in god serves some positive purpose at times (such as giving hope amidst utter despair), but overall I think the negative weighs in more than the positive. I believe each person has their own god and religion within themselves and it would behoove us all to find it through some serious introspection.
At a more epistemological level, I think all existence is random and inherently meaningless and purposeless (so even if god existed, god has created our universe to be this and is probably just as surprised as us that something like humans sprung up). I think humans tend to lend purpose to their lives by imbibing it with some artificial meaning: in terms of asking and answering questions (science and philosphy) and creative endeavours (arts), through love and relationships, and through god and religion. This in and of itself isn't bad, but given the objections I've stated above as to what a belief in god and following a religion can cause and has caused, I see reasons against being a theist and thus I've chosen to be an atheist.
I'd like to make a note on language: I don't capitalise the word "god" because that would limit my discussion to monotheistic religions/beliefs. I also don't attribute to a sex to a god (again, a concept of monotheistic religion) preferring the gender neutral term "it". My discussion in general applies to any "higher power" being that lays claim to being the arbiter of what is wrong and right for sentient beings.
In certain religions, god is omnipotent. How would such a god answer this request: could you please create a stone so heavy it cannot be lifted by anyone, including you? Such a god that creates a universe which it cannot control (or where free will exists) is a contradiction.
Another interesting question to ponder: can god sin? Especially consider the fact that man (who supposedly sins) is made in the image of god.