There's a very good reason for teaching people that violence is the absolute last resort that should never be tolerated except under the worst conditions. It's because people are stupid.
If you taught them there were any lower of a threshold for violence, there would be violence over anything. Violence is already extremely commonplace. So is political anger. Do you really think we would be better served by an even more volatile populace?
Political violence is rarely a positive thing. It can be, sure. But history is full of examples where revolution lead to greater tyranny. I'd rather the average person realize that they aren't intelligent enough to make the average political system better with violence. They're a lot more likely to make it worse without very judicial application of violence, and leaders who know how to make the most of what is left behind after the violence ends.