[James]

Protests rarely change anything to policies in democracies. What does makes a difference is public opinion.

Ultimately it is about votes in elections; even when an election is a long way off, politicians (as much as we don't want to believe it) are conditioned to respond to shifts in public opinion.

For example the pro-EU rallies didn't reverse Brexit because they didn't demonstrate a change in public opinion - it was just the people who supported Remain before and were passionate about it out on the streets.

Violence and destructive protest can have a negative effect and it is usually unjust. You have to say it is often carried out by a minority, say, 10% out of a crowd of thousands.