Edit: For those downvoting, is there a problem with considering this possibility? I think it's incredibly unlikely, but ignoring black swans can one day come back to bite you. Ideally, everyone should be aware of the theories out there, however ludicrous, on the off chance that they are correct and require critical and swift action.
That contains as much conspiracy as "somebody is hunting down the protestors".
There are simpler possible explanations, I believe, e.g. people who join (or organize) riots are usually not the stable boring kind that live long, predictable lives full of planning and quiet afternoons. Drugs, crime, violence and mental health issues are probably more prevalent in that group than in the general population.