Because it gives those without a voice or influence some sort of pressure-relief.
That being said, it's unwise to riot in this day and age, what with the hypermilitarization of police and law-enforcement, not to mention the bought-and-sold judges.
We, the people, have nothing to bring to the field that even compares to what the protectors of the parasites have. We have only out numbers and our labor. So why not use our weakness as a weapon?
The system seems all-powerful and inescapable. That's a fallacy. The system, in order to function, has to be paid with something (be it labor, energy or money). What do you think would happen if a thousand people in a community would stand up and say 'No. I will no longer play this game.'?
Because that's all it is, folks: a game and the rules are ever changed in your disadvantage. There is absolutely no reason nor obligation you should paticipate in any system, in any game if you choose not to do so.
You want to stop this system? Then Stop Playing The Game.
Say 'no.', be it against police invasiveness, random stop-and-searches, video surveillance, whatever.
"No" against the politicians who are either inept, corrupt or clueless.
Do not pay taxes if you have no say in what they are spent on.
Or better, stop participating altogether: get your community together and talk amognst yourselves how you wish to govern yourselves and then do so. Imagine a thousand people knocking politely on the door of city hall, giving the politicians their 2 weeks notice WILL make an impression,
Of course it's illegal to fight the system, that's why the system made it illegal. But as long as you remember that all it is are just lines on a piece of paper, and nothing more, what power do these lines have over you, should you choose not to participate?
You want this system over? Imagine that you could stop paying for it then, with your taxes, VAT's, whatever. Barter, Grow it yourself. Make it yourself. Cooperate with your friends, family and neighbours. And when the system comes knocking, ask who they think they are since they've made an almighty cock-up of the whole situation in the first place.
Imagine what would happen if you do not lose your calm, but remain honorable, polite and in good standing. Yet equally politely tell them you do not participate. What can they do? Lock you up? You're already in a cell, albeit with bars you cannot see.
Will return later with a more thorough rebuttal.