That's a pretty uncharitable interpretation of parent's comment. I read it as "to protect bystanders and property from the mob [that was violent]".

And his point seemed to be that police being "noticeably absent" from peaceful protests is more simply explained by the fact that those protests were peaceful rather than police presence being the source of violence.

Police brutality is a real issue but indiscriminately blaming the police every time they show up doesn't help the cause.