Not for lack of trying. I've seen them kicking people on the ground. It only takes one hit to the head, nose or neck to kill someone depending on the force.
Only because their would-be victims get pulled back by eagle-eyed people behind them. Another hit and that Antifa bike-lock wielding prick would have potentially killed someone.
Bet if someone related to Antifa did kill someone you'd pull the same 'Not all Antifa' shit though.
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Communism has killed more people than Nazism. Their historical record speaks against them. Unless you don't think what Mao and Stalin did can be compared to modern 'communists' in which case Hitler and the National Socialist party can't be compared to todays right, alt-right or far-right political groups (also I like how anyone even remotely right-wing gets called a Nazi instead of just the far-right lunatics. Really gives me a chuckle).