Militant atheism can also be problem (like in the Soviet Union). However there is no doctrine in atheism that states that atheists must eradicate theism or they will go to some atheist hell, hence despite the fact that atheism is not logically compatible with theism, it can tolerate theism in action.
Actually, there is a motivation for atheists to press their belief on others. Atheism is an inherently supremacist belief system, since it is basically always justified with some sort of reasoning. While I'm sure there are some atheists who simply don't believe with absolutely no reason for it, the vast, vast majority justify their beliefs with some kind of reasoning.
Sure, you can have supremacism in religious belief, such as islamic extremists who try to press their beliefs on others, but the difference is that it's not inherent. When you literally have no reason to believe what you believe, it's hard to rationally argue that your belief is superior to anyone elses. This is contrasted with the supposed superior beliefs of atheists, which they have reasons for.