I'm not advocating either side, but what I would like to talk about is the protection and fostering of ideas.

The police officer was defending( if this is the US...pretty sure it is...but can't assume anything these days) the idea of the freedom to assemble and free speech. Even terrible people deserve these rights, otherwise we are just as terrible as a society.

He wasn't trying to end his life for the flag, it's highly unlikely he wanted to kill him. He was attempting to keep peace, a threat of violence stops these things quickly. Plus, the officer doesn't know if this is a rational person who wouldn't escalate the issue past stealing a flag, or if he is on drugs and is carrying a weapon because he was planning this ahead of time. Imagine you're the police officer and you know the threat of death is out there and people would rather kill you than go to jail even for small crimes. This is especially true of people under the influence of mind altering substances to include alcohol. Would you not fear for your life, or go survival if a man goes to steal a flag in such a manner? What would you say about him if he just stood by?

He had a choice. Either stop the man from possibly hurting others, or giving others the idea that this sort of behavior is ok. Or, do nothing and risk the protestors escalating the issue themselves. All the while trying to keep himself safe. I don't think it's an easy job being a police officer, what is easy is being a critic.