Not all riots are bad and not all riots are good, it is a matter of perspective.
What isn't open for debate is that riots happen when people are simply fed up with the system or something in society. These can be for good or bad reasons. There has been racist and violent riots that turned into massacres of minorities and there have been riots that has verged on entirely justified following decades of built up systematic oppression, like the stonewall riots that kicked off the gay rights movement.
People also have a tendency and natural bias to excuse public violence and disorder when it is in response to a subject they find objectionable. I admit I do that when I think of the stonewall riots. When something matters deeply to you, it can actually be deeply comforting to know that at some point people were mad enough about it to riot in the streets. Riots are probably best described as a form of mass catharsis for participants and sympathetic observers. The price of this catharsis varies widely, but usually it comes at the expense of the rioters own homes and communities.
That said, I do question how effective they are at changing public perceptions. If someone wasn't on your side to begin with, getting violent publicly is probably not going to effectively sway them toward you. I don't think that thought generally enters the heads of rioters. They just want to extract some kind of price from society be it in destroyed property, obtained loot or even just forcing the other side to stop you if they can. It is an exercise in power, which is why we so often see it be employed by both the outraged powerful seeking to reclaim privilege and frustrated the powerless. The message it sends is that we are stronger than you think and we won't take this anymore.
One thing I find troubling is when we infantilize rioters. Rioting is a decision made by everyone who takes part. It isn't ever fair to classify it as entirely a reaction to the behavior of others. When we riot we ought to own what we are rioting about and claim responsibility for it. If it was worth rioting about it was worth deciding to riot about. Shifting the blame to the other side for causing it, when you are the one doing it, is most certainly not a strategy that convinces many neutral observers.
Just my 2 cents on the matter.
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