You know, I just can't. Biden is a scumbag to be sure. Biden is not Adolf Hitler.
Now, some of his supporters (like Antifa and BLM) sure seem to act like Brown Shirts, though I think that a better comparison might be the Red Guards under Mao.
Though, ultimately, the right doesn't even have the option of misbehaving as much under Biden (in the terrible but likely event he wins) as the left did under Trump because we don't control the media, we don't control the nation's powerful institutions. When right wingers beat up people in the streets they go to prison for years instead of having charges dropped. The right can't smear Biden with nearly every media outlet, can't have social media censor Biden supporters, can't trump up charges against him to terrorize his allies and distract him from his agenda.