The definition of 'faith' is "belief that is not based on proof". Can you prove that God does not exist? You can't, hence atheism is faith. This statement alone would be very controversial so let me elaborate.
I think your objection as an atheist to this statement might be that you've always maintained that atheism is the neutral position and now suddenly I'm bringing that into question for you. However, the fact that atheism is a belief does NOT depreciate atheism or the arguments for it. An atheist is still a non-believer and it's a very rational position to take. If however you feel uncomfortable with the idea that there is no evidence of the non-existence of God and therefore atheism is faith, perhaps you will find comfort in considering yourself an agnostic and anti-theist. Let me elaborate on that.Agnostic
Most atheists consider themselves atheist because they don't see how God could be real and I take that position as well. Someone recently told me there are two forms of atheism: weak or agnostic atheism ("It's possible but unlikely for a god to exist.") and strong or gnostic atheism ("A god does not exist"). If you state that God does not exist that's not a fact because facts need to be proved and by definition God can't be proved because it's exterior to our universe, just like a multiverse can't be proved (but can be strongly suspected by association and experience) because it's exterior to our universe. If you state that God does not exist that's a personal conviction/opinion. So, if you're a weak atheist your position is hard to argue. If you're a strong atheist then that's based on an opinion and takes a leap of faith. I can find myself in weak atheism also known as agnosticism. What might bother you about considering yourself to be an agnostic is that it implies that you're open to the possibility that God exists while the idea of God just seems ludicrous to people who would consider themselves to be an atheist. This brings me to anti-theism.Anti-theism
Anti-theism can also be defined in two ways. The anti-theist can detest religion (which many atheists do as well) and he can detest the concept of God. I personally detest both. Even if God could exist, I maintain it's a horrible idea. So anti-theism doesn't pretend to know God does or doesn't exist but expresses an opinion. To consider yourself an agnostic and an anti-theist tells the whole story: it's highly improbable that God exists and in my opinion there is no way and no reason for God to exist. I think this is essentially what you mean to indicate with atheism but described in a more descriptive manner. 'Atheism' can imply things you don't mean to imply.
I'm rather reserved in making statements which haven't been proved, and to consider myself an atheist goes against the scientific protocol. This was also Carl Sagan's opinion which is why he said the following:"An atheist is someone who is certain that God does not exist, someone who has compelling evidence against the existence of God. I know of no such compelling evidence. Because God can be relegated to remote times and places and to ultimate causes, we would have to know a great deal more about the universe than we do now to be sure that no such God exists. To be certain of the existence of God and to be certain of the nonexistence of God seem to me to be the confident extremes in a subject so riddled with doubt and uncertainty as to inspire very little confidence indeed"
However, in practice Carl Sagan could definitely be considered an atheist in the general sense of the word. He preferred not to consider himself as such because it goes against the scientific protocol, which needs to be kept in honor especially by a scientist. Neil deGrasse Tyson has a similar opinion on the matter as he prefers not to consider himself any -ist except for 'scientist'. I strongly recommend you watch this 4 minute video to hear what he has to say: www.youtube.com/watch?v=CzSMC5…
On this note, I'm not quoting people of authority to give credit to my statements—or worse, to pretend that I'm correct. However I do want to show that I'm not the only one who makes these distinctions.
I very much respect atheism and in practice I am an atheist but I have to be reserved with my statements because I simply don't know. To give an analogy, when a black hole was described in mathematics many scientists were convinced that black holes had to exist while others thought it was too weird. It brought a great divide within the scientific community. What would be wrong at this point though is to state that black holes ARE real. Even though we now know black holes do exist, there was no observational evidence for it when the concept of a black hole was first described. Scientists had to wait for observational data until they could state it as fact. Equally, I rather wait for the observational data of God before I can state with absolute certainty that God does not exist. Meanwhile though, it's my opinion that God does not exist.
I personally think a bit of controversy is good so we can have a well-mannered intellectual debate, however of course not just for the sake of it; it needs to be productive. According to my reasoning though atheism is based on faith. But again, this notion doesn't depreciate atheism, and atheism is definitely NOT a religion. I have to bring very strong emphasis to that distinction.