Animate any "cause" shared by just about any sized group of people, no matter how absurd the cause. In this case, something that guys always found kinda embarrassing. In my experience such people tended not to advertise their lack of prowess in this area. Now, they can go somewhere virtual and commiserate with each other, then do the usual when unhappy with a situation (blame others for it), then keep reinforcing each other until they feel truly aggrieved and persecuted by these outside antagonists. Eventually, action to address the perceived "persecution" gets more and more likely.

Along the way something once to be hidden in embarrassment becomes a cause to celebrate. Here, celibates who think women are unfairly conspiring against them, I guess. Last summer in Cville, racists proudly wearing their racism for all to see. I think this asshole in Pittsburgh sees his murderous rampage as something noble. For him, immigration seems to be what set him off.

Trump isn't responsible for Bower's actions, but all this shows the power of the Internet as a tool of demagogues.