So here's an
amazing analysis from Reddit about the issues concerning tribalism, the Left and Right.
I'm just gonna post it in full. (It's a tendency of all the "big" media outlets to steal shit from Reddit; at least I'm properly crediting it.)
All I'm saying is if someone does something bad in a protest, that doesn't make the protest bad.
I think you've chosen the wrong argument here. I think what you should say is that the reason for the protest might not be wrong just because it turns violent, as in the position or argument that the protestors are basing their protest on can stand regardless of the protest actions. That could be true.
However, a protest is what happens at it. A protest that turns violent is, by definition, a bad protest. There is a difference behind the position of the protestors and the behaviour of the protestors. Bad behaviour doesn't mean a bad position, true, but the protest itself is the behaviour, not the position. You can hold the position with or without protesting. The behaviour is the protest and the protest is the behaviour.
Being "in the right" or "in the wrong" is also multifaceted. If I tell you that 2+2=5 and you say, no, it's 4, and I disagree, so you punch me in the face, then you are factually correct in your information but morally wrong in your actions on how to convey that information.
Beyond that academic discussion, there is a deeper issue though. Resorting to violence itself tends to come from a few main sources. People who resort to violence generally often can't win the argument on merits and get frustrated, so turn to violence because they truly believe something even if they can't demonstrate it to be true or articulate it. For example, the claims that Milo is a white supremacists, racist, sexist/misogynist, Islamophobic, or otherwise are baseless because there's both no evidence of any of that and there's plenty of evidence he isn't. But, he tends to vehemently criticize the "social justice" left, so they hate him and either tend to shout him down or turn to violence, since they can't win by debating on facts and reasoning. (I say this as somebody who disagrees with much of what Milo has to say in academic terms, but his critics are more wrong than he is.)
Essentially you can create hatred, vitriol, and violence between groups is two easy steps. Step 1 is to divide people into groups. That can be random as in the RCE, arbitrary such as the eye colour in Jane Elliott's classroom experiment, or essentially any differentiator: political leanings, favorite sports team, religion, nationality, accent, height, PC vs Mac, Android vs iOS, Coke vs Pepsi.
Step 2 is to set the groups in conflict, either via a competition (rewards, punishment, social status, attention, special privileges, etc.) or sparked by group-based insults ("fascist right", "communist left", "criminal blacks", "privileged whites", "terrorist Muslims", etc.).
That's it. Then buy some popcorn and watch it degrade into violence. In the RCE there were fistfights, sabotage, burning of other teams flag, and so on. In Jane Elliott's class, the different groups oppressed each other given the chance.
In addition to the violence and hatred, the groups tend to create in-group social norms arbitrarily and out-group narratives, typically with "us" being saints and righteous and "them" being evil. Both sides tend to rationalize, including rationalizing violence because "they" are evil, and the ends justify the means. Facts be damned.
In the U.S., this tribalist behaviour is
clearly demonstrable in the massively partisan division. On top of that, you have the fringe voices becoming the justifications. On the fringe right you have the white supremacists who statistically represent a small rounding error of Trump supporters yet these are who the political left use to smear Trump supporters. On the fringe left you have the "social justice" activists and anarchists who represent only a fraction of the anti-Trump crowd (and/or Clinton supporters), yet this is who the political right use to smear anti-Trump supporters. (Milo is one of them too, who equate SJWs with liberals or anyone left of center, which is where he is very wrong of course.)
It also happens that these are the two groups that instigate Steps 1 and 2 of Realistic Conflict Theory. The fringe bigots on the right group people by traits: skin colour/race, sex, sexual orientation, gender identity, and so on. They put them in a competition in a hierarchy with the dominant/majority at the top and the marginalized minorities at the bottom, and suggest everybody must conform to the interests of people at the higher end of the hierarchy.
The social justice left also group people by traits: skin colour/race, sex, sexual orientation, gender identity, and so on. They put them in a competition in a hierarchy with the marginalized minorities at the top and the dominant/majority at the bottom (known as the
progressive stack), and suggest everybody must conform to the interests of people at the higher end of the hierarchy. And, they refer to groups having "voices" and treat people based on their grouping. It tends to derive from a form of Marxism of flipping the powers as applied to minority status instead of by peasants vs industrialists.
Voila, both of these fringe groups both contribute to creating hatred between groups. Both contribute to each others existence and power, and both pull the partisan politics to more extremes. And both are very, very wrong. Both commit the
fallacy of division, assuming things that apply to the groups as a whole apply to individuals described by those groupings, and both commit the
base rate fallacy. The fringe right confuse the fact that "most terrorists are Muslim" (true) with "most Muslims are terrorists" (not true). The fringe left confuse "most privileged people tend to be whites/males" (true) with "most whites/males tend to be privileged" (not true).
The correct answer is for both fringes to stop treating people as being part of a group defined by traits, and instead treat people as individuals who have traits. Treat them by the content of the character (merit), and not the color of their skin (race). This is, in fact, what is written into human rights codes, that all individuals are equal to other individuals and have the right not to be judged based on such traits, except where the trait is the merit of interest itself. It is then violations of that rule that are bigotry, and that applies equally to all people of all races, sexes, gender identities, nationalities, ethnicities, and so on. It's the violation of the principle that matters, not the particular race or group that matters.
So what does this have to do with violence and protests? Protests often turn violent when the protesters are themselves subject to tribalist tendencies; the "us vs them" mentality. This is why right-wing racists turn violent against racial groups and fringe left-wing groups, and why left-wing Marxists tend to turn violent against right-wing groups. It's also why liberals, libertarians, and moderate conservatives don't tend to turn violent, because they are based on common rules for all and equal freedom and equal rights for all, not group against group fighting for power.
So, in that context, a protest turning violent is an indicator that the protestors are not doing so based on taking a reasoned position, but rather are being tribalist. It's not so much your example, "if an anti-fascist protest happens and a protestor punches someone", it's more that the "anti-fascist" protest is very likely wrong that the people they are protesting are fascist at all.