There are extremists and fringes everywhere. I’m sure there are atheists that say all kinds of stupid things. But that’s not what atheism IS.
Atheism is better understood as a philosophy that says, “The proper way to understand the universe is to apply the scientific method. We must demand proof, experiment, falsifiable predictions, and the other tools we have developed over millennia to help us sort out fact from fiction.”
The reason atheists don’t believe in God is simply because such a belief doesn’t pass those tests. But it’s not a dogmatic belief: If someone came up with a strong proof of God’s existence, and it could pass the tests above, atheists would have to admit that there is a God.
But that gets us to a paradox. If God is defined as a being that transcends the laws of men and the universe, then he’s outside the realm of science anyway, which means we can’t ‘prove’ his existence. And evidence to the contrary can always be hand-waved away as having been placed by God to test us. It’s an unfalsifiable theory, so for people who use reason and science to puzzle out what’s going on around us, it’s becomes a question that’s not even worth entertaining. When come back, bring evidence.
To me, the difference between agnosticism and atheism is that agnostics weight the possibilities of God/no God equally. So an agnostic might say, “There might be a God, there might not. But both propositions are worth equal attention, and I’m keeping an open mind.” An athiest would say, “I have no reason to believe in God, so until someone gives me a reason I’m not even interested in the question.”
Or another way of looking at it: Agnostics have an open mind about the existence of God, but atheists employ an entirely different epistemology that explicitly rules out belief without evidence, so the question of God is moot.
But I’ll bet you even agnostics are atheists when it comes to believing in Valhalla, or volcano gods, or the existence of fairies and pixies. And I’ll bet most Christians are too. Or should Christians keep an open mind and say, “Well, I’m not sure… Baal, Jesus… I’m in Jesus’ corner right now, I have an open mind and am willing to be convinced that I should throw my first born child into the nearest volcano.” I think not.