on your first point, I wonder: are the Greek authorities worried about the strain (I actually first typed "stain"!) on the ability of the police to effectively fight real crime while hundreds or thousands of its force are dedicated to the violent assault of peaceful protesters?

They oughta be. But that's not the protesters' problem.

Another problem is that police then know that they are relied on in that way in that situation, then they get to think that they have licence in other situations.

Any idiot can face a crisis - it's day to day living that wears you out.