Amidst the disturbing trend of political conflict in the United States escalating into violence, it has been a staple of conventional wisdom that the real danger comes almost entirely from the far right. Thus, after journalist Andy Ngo was beaten up by activists from the militant left-wing “Antifascist” movement at a protest in late June, commentators such as Vox’s Zack Beauchamp cautioned against attempts to portray Antifa’s record of violent behavior as even remotely comparable to that of far-right extremists. Beauchamp quoted an Anti-Defamation League primer on Antifa which said, “To date, there have not been any known Antifa-related murders.”...