Atheists don't fight for nothing. They fight for the truth and against ignorance, which ultimately hurts people more than it does good.
Also, who said atheists believe in nothing? There are Agnostics aswell... And Atheists who simply wont dare assume they know the truth about things they have no proof of.
Some religious people on the other hand, will blindly believe in religion because it's comforting, despite it being disproved and questioned against in so many ways.
Really.. Atheists wouldn't care much either(well many of them wouldn't I guess.. I can't speak for everyone), if it wasn't for the fact that religion has so much negative power over the world.