I can prove I didn't commit a crime by supplying an alibi. I can also show that the laws of the universe are such, that they do or do not support a particular claim. So there are in fact ways to prove, at least, certain negatives.
If you cannot prove there is no God, then how can you claim there is no God? All you can do is state that you believe there is no God, making atheism, a belief system.
See
here and
here.
True, it's only non-contradictory universal negatives that can't be proven. I can prove there's no unicorn, as usually described, in my attic. I can't prove there's no unicorn anywhere in the universe. If the unicorn has contradictory attributes, we can establish it doen't exist anywhere in the universe because the concept of unicorn is incoherent. Now if the description of the unicorn were falsification-proofed the way God's is (can't be detected, doesn't act overtly) I can't even prove one's not in my attic. Define God and we can talk about whether your version contains contradictions.
My statement is that I don't believe there is a God. Not having a belief is not a belief. One belief does not a belief system make. So you fail on the belief system claim on two levels.
Just because I have doubts your legitimate faith will allow you to understand my point, I will illustrate: The difference between not believing in God and believing there is no God is similar to the difference between not believing you have a fifty dollar bill in your pocket and believing you don't have a fifty dollar bill in your pocket. Get it?
And just because you may not be conscious of why you desire atheism to be a belief system, I will explain it to you: you know it's reasonable not to believe something based on inadequate evidence, which is the position
you are in; and what you are fundamentally trying to do is level the playing field by claiming that our postition is also an unjustified belief, and therefore just as weak as yours. 'So are you!' is not a valid argument, that is, even if true it doesn't support your position.
Besides lack of evidence, the main thing that persuades me God is highly unlikely is that even people of self-proclaimed legitimate faith seem to be unable to present an argument for existence of such a being that doesn't contain a fallacy. For instance, your 'legitimate faith' argument is a non sequitur: even if true, it doesn't follow that God exists, the most you can establish is that certain spiritual practices result in people being consistently good. In fact, these practices having the same result for people of different faiths indicates that it's not the object of these faiths that matter, it's
how they believe whatever it is they believe.