> I don't understand how local governments could possibly lack the authority to remove people from public spaces.

We seem to forget these days that we (very thankfully) have rights and live in a free country that recognizes them. People are free individuals, at liberty to do as they please unless there is some strong reason to stop them that is also constitutional, lawful, and follows due process. 'I don't like them' and 'they look/smell/talk funny' aren't sufficient reasons.

I don't see how local government has the authority to remove someone from public space except in very limited circumstances. Public space is not the property of local government. You have a right to do what you want there.