Just like religion, the problem with atheism is not the [non] religion but the people. For me atheists people who hold dear the principles of harmony, do good to other and apply the Golden Rule, are acting like a good Christians and good Muslims. It's the right kind of atheism.
But just like in any religion, there are those who are badmouthing even insulting other religions, and force people to see everything from their point of view / scripture / principles / version of religion.
This also applies to atheism. So the argument is not about religion vs non religion, but it's about persuading people to subscribe to their point of view. To me, this is the definition of extremists. And there's such thing as atheist extremists.