Most young atheists, at least where I live, are pretty upset about being treated poorly, lied to, shunned, mocked, etc for their lack of belief. They are angry at being told by christians that they are going to be tortured for eternity. They are upset that the people around them trust them less than they trust pedophiles.

This anger and resentment that many young/new atheists feel towards their oppressors often boils over in anonymous forums online where they can freely and openly express themselves without fear of hatred, violence, and mockery for the first time in their lives regarding the topic of religion.

It's a stress relieving response to christian bigotry and hatred.

Does that help answer your question?