I'd say require the police line to wear body cams, have them on, and then require connecting a shot to a specific act. That would also serve as good Pavlovian training for people who think violence is ok as long as they personally think it's ok. The definition of what act can vary, but what I meant above is limited to this instant, targeted reaction - what I want to see is a specific "protester" throw a rock at police, or force entry, or set something on fire, and instantly gets shot; with camera evidence of both. Of course, I'd also accept arresting (and prosecuting with real punishment, not releasing after a few hours), but I don't believe it matters which one is used in the case of violent riots.
It matters a lot when you decide that rioting people can simply be shot. Because it means you've given them up as humans. One of our claims to civilization is that we handle violence sufficiently, not proportionally. And certainly not excessively.
That's incredibly scary you hold that view: You're suggesting massacring protesters who are only causing property damage. Tear gas, rubber bullets and pepper spray are the way to disperse mobs/protesters/rioters from causing excessive property damage.
Of course if some protesters started shooting people then obviously using lethal force might be required.
I mean, get real. You can't just shoot people for breaking windows or stealing. The fact that this is unclear to anyone is appalling.
In this case we are talking about trying to achieve political means via violence. The kind of people who do that outside of very extreme circumstances definitely renounce their moral value as human beings in my view. It's not that they /should/ be shot as a punishment or something; it's more like dealing with malarial mosquito - the evil is on the level where ends justify the means.
Your logic could be applied to any number of movements, including the Women's Suffrage movement, the Civil Rights movement, the Revolutionary War, and thousands more.