Reading through this article and other sources I've read, I get the sense that the antifa are a reactionary force. Their methods are not necessarily welcome, and escalation in a conflict is an issue.
However, historically the fascists on the right are the ones to start the fight. They work toward the breakdown of civil discourse in society so that their methods of brute force seem more appealing and have less opposition through discourse or argument. They create the conditions which then encourage reactionary groups to resort to violence as a last resort.
That's one major reason I've been so dismayed and angry over the Republicans' efforts to destroy civil public discourse through their propaganda and other means. Because when civil discourse breaks down, you open the flood gates to shit like this. But they know they can't survive in an environment where facts, evidence, and reason are respected.
I don't like that antifa and related groups resort to violence against extremists on the right, but I see it as inevitable once civil discourse breaks down. I'm all for protecting civil discourse no matter what, because what comes after is never good. But I also agree with the antifa groups arguing that after that point, stopping the right wing extremists with whatever means possible as a last resort makes sense. As we've seen in history, the cost of allowing them to continue unabated can be devastating.
My ultimate position: don't let idiots break down civil discourse to begin with and you'll avoid the reactionaries resorting to violence and other means. Yet, in most cases, it seems to be the right wing extremists that start this shit by breaking down civil discourse. I don't care what side someone is on, but it's best for everyone if civil discourse is protected at all costs. Otherwise, things just break down from there.