Why do atheists always attack Christianity on here?

Is it because Christians are the only theists in R&S (especially since the Muslims all retreated to and barricaded themselves in Ramadan), or because they are the most vocal/visible theists here, or because they have the weakest arguments, or because they are the most fun to troll, or because they know about Christianity the most, or because Christians usually believe in freedom of speech and thought, and normally don't go ape**** whenever their beliefs are questioned in any way?