Sioraf... I have no idea where to start... you tote logic and philosophy as weapons but you've been wounding your argument with them more than you've been helping them. Do you have any education in logic or philosophy?
Let me put your arguments into two syllogisms. Correct me if I've interpreted them wrongly. Obviously I've simplified them, there are a few other syllogisms between, but I feel they're trivial in comparison.
Premise. We humans are imperfect.
Premise. There must be an underlying balance to our imperfection.
Conclusion: There must be a perfect being to balance out human perfection, this being is God.
Firstly, if there must be an underlying balance, why would perfection balance out imperfection...? Secondly, I agree it would be acceptable to call a perfect being God, but since you are a Catholic, how does this perfect being translate to the Catholic God, especially when the Bible shows many instances of God's imperfection. Why can this God not be the Islamic God, or the Hebrew God, or even the Protestant God? Of course, the main issue with the syllogism is the second premise. Your idea of underlying balance seems to be completely intuitive, and not on anything concrete. What gives you the impression there must be a balance? I have a feeling you'll say something along the lines of "it would be illogical for there to be no balance", which brings me to your second main argument.
Premise: Everything must have purpose, it is illogical to assume otherwise.
Premise: Humans exist.
Conclusion: Humans must then have a purpose.
Once again, I take issue with one of your premises. Why is it completely illogical for there to be no purpose? I believe you are assuming this based on your intuitive idea of the universe. It's probably quite ingrained in your mind. I would argue that existence is contingent, and that it inherently has no purpose. We are all simply the result of a long chain of cause and effect resulting from the laws of physics, etc. Our purpose isn't necessarily to reproduce and survive, as per evolution, it's simply that as living organisms that have a drive to reproduce and survive we have more of a tendency to exist than does an organism lacking this drive, and we can't observe what does not exist. We exist because we're good at existing. This may sound bleak for someone who's long been on the drug of religion, but what it means is that we have no external purpose that forces itself upon us. Rather, we are free to make of our lives what we will. We are in a unique position to choose to continue to exist, and to choose how we go about our existence, and to choose our purpose.
I was a little miffed by your idea that these should be argued upon grounds of philosophy rather than science... there is no dichotomy between philosophy and science. The scientific method was the result of naturalistic philosophy, and science offers many of the premises upon which modern philosophy is based. Of course, if you truly want to argue on philosophical terms, try reading the large body of atheistic philosophy that exists... say... atheistic existentialism...?
Apparently you've been ignoring Archonix, because you keep saying that we atheists are simply sheep reciting groupthink and that we have yet to disprove the existence of God, but simply criticize various doctrines of Christianity... Even if a God existed, there is nothing to suggest that we would naturally have a belief of God. This is evidenced by the millions of atheist children brought up in non religious households as well as the great variety of gods, monotheistic and polytheistic, that everyone else ascribes to. It may be hard for you to imagine not having a concept of God but that's because it's potent idea that's floated around our culture and is nearly inescapable. The burden of proof does not lie with atheists, but with the religious, because it is the one that is introducing a supernatural being and a set of rules that must be justified. Saying that we have yet to disprove God is like saying we have yet to disprove the Flying Spaghetti monster. We can't consider every supernatural notion anyone has, let alone disprove it.
When you understand why you don't ascribe to the plethora of Gods that have been worshipping throughout history, then you'll understand why we don't ascribe to yours, or anyone's.