Anon, offensive humor has long been part of the chans. "Get the high score" (video game reference–see pic related) is an expected response on /pol/. I'm not going to claim that's a morally acceptable or tasteful response to a mass shooter, but that's part of the chan culture in general. Offensive humor, extreme racism, and gore were always used as a filter to keep the "normies" and weak-stomached people away.