You’re wrong about people knowing that they’re going to be arrested for many protest activities. The point of marching is that it doesn’t damage anything and it doesn’t hurt any people. That’s why people go out and they walk in public places and on roads and on bridges, because it doesn’t harm anyone so there’s no reason to arrest anyone, but it does make their presence felt so people can’t pretend the problem doesn’t exist.

If your solution is that anytime a protester does anything disruptive, they should be arrested, that will encourage all protesters to immediately move towards property damage. If they’re going to get locked up anyway, why not break the windows of the companies that they think are doing such a bad job? Why not burn a few police cars? Then they’ll be making the presence felt and taking funding away from people who don’t deserve it.