Because they are immersed in an ecosystem that pretends that respect for human dignity and unearned respect for authority are identical because they use the same word.
They believe that others should respect the innate authority they feel they should hold as men. Simultaneously, since they don't get that, they don't feel like they need to respect other people's right to exist.
And then a group promises them everything they've ever wanted, if they are willing to do fascist shit. Of course they're into it.