The Internet has enabled the flourishing of countless subcultures, from the harmless to the less so. Lately, one of the latter groups has begun to break into the mainstream: the “incels.” “Incel” is short for “involuntary celibate,” and as their self-imposed name implies, these mostly young men have come to define themselves by their inability to find a sexual or romantic partner. Men who identify as being #ForeverAlone have gathered online in forums such as Reddit to trade stories of woe. These communities tend to be self-reinforcing. Members believe that their looks or personal traits have consigned them to lifelong...