Gavin Mccines was scheduled to give a speech that night, which he did. Some of that speech involved a play of sorts, in which some of the Proud Boys were participants. It was also known before hand that Antifa was going to show up to protest. Mccines had the police there for the purpose of protection. Antifa members were there instigating things for hours. After the speech, when Mccines and the Proud Boys were leaving, one of the Antifa guys bypassed the police to grab a MAGA hat off of one of the Proud Boys and took off running with it.
That 2 minutes of video showing the Antifa guys getting their asses beat down was the only thing that made its rounds in the media. So of course, it's going to look like these guys are extremists who just go around looking for Antifa guys to beat on. They didn't report on the hours of instigation, prodding and teasing by Antifa beforehand.
The basic thing behind the Proud Boys is to be unapologetically male in the face of feminism, toxic masculinity, political correctness, etc. It is easy to paint all of that as cult-like, extremism from a more progressive point of view (especially given that Mccines is the type of guy to say that women would be happier at home in the kitchen vs. the workforce).
From what I know, it is no more of an extreme fraternity than the kinds of things discussed collectively by members here at SS, the only difference being that their focus is not on picking up women, but is more about conservatism/politics in nature.