Provided the fact that Atheism is usually defined as non-belief they sure make a whole a lot of fuss over their non-belief.
It's almost like billions disagree with them, and even hold it against them, and they want to encourage each other, discuss paths for moving forward, etc.
Those who disagree with Atheists usually admit out lout that they most certainly believe in something. Sound more reasonable to me to make a fuss over something that one believes in rather than to make a fuss over something that one doesn't believe in.
If you didn't believe in UFOs, but the majority of people on earth did, and you were denied employment and such because you didn't believe, and you were derided by family members, and forced to put up with constant condescending comments about how you just aren't intelligent enough to see the truth, and oodles of money were being spent on belief in UFOs unnecessarily, and people who believed in UFOs were holding back real research in science, and... well anyway, if you were in such a position as a non-believer it might not seem strange to organize with other non-believers and see what you could do about the perceived problem.