Antifa are (as the name should have suggested) specifically targeting what they perceive to be fascist groups, were you so desperate to virtue signal using the term "virtue signalling" you forgot to read the OP?
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Metal is pretty SJW friendly for the most part; having had genuine problems with fascism, misogyny and racism from some parts of the community metal-heads tend not to be so overly sensitive and easily outraged when people criticise aspects of the sub-culture.