Atheism is the belief that there is no god. Whether this is based on science or not is irrelevant to the classification. They believe, rationally or irrationally, that there is no god, nor gods. That's what the word literally means. No God.
Agnosticism is accepting that one does not know, and therefore withholds judgement. Agnostic means, literally 'Doesn't know.' One can believe there is a god, but not be sure, and willing to be skeptical on the issue. This is agnosticism. On the other hand, one can believe there is no god, but not be sure, and willing to be skeptical on the issue. This is also agnosticism. It does not matter if you believe that it cannot be proven... all that matters is that you believe it has yet to be proven.
There are subsets of these camps. There's some atheists who simply do not believe in a God or Gods and don't care what other people do. There's some atheists who believe it is irrational -to- believe in a God or Gods. And there's others still who believe in some other supernatural stuff without believing in higher powers.
Just as there's some theists who believe that Jesus saved us from our sin by his sacrifice, others who believe that the world was created when two four-armed gods did the horizontal dancing, and others still who believe the world is guided by some janitor named Bob who does so with the power of his mind through his TV set. And there are some who bomb, kill, murder, slander, and express hate. And others who express love.
I believe personally, that some religions are harmful, others can be helpful, and that no religion should ever be in charge. I believe in the value of freedom -of- religion, which must mean freedom -from- religion.
And I believe that there are no absolutes in such arguments. Some atheists are incredibly moral individuals, others are destructive and misguided. By the same token, some theists are truly awesome humanitarians, and others are homicidal dicks.
And I believe the existance of the dicks is not proof against the validity of either view; otherwise by that logic -both- views are utterly destructive and therefore believing in anything is destructive. Therefore we must not even accept our own senses, and the world therefore must not exist. But because this belief has proponents that are destructive, that is also proof that believing in neither side is destructive. And non belief is also destructive. Therefore everyone is destructive by nature.
See. Logical fallacy.