Isn't the First Amendment for everybody?

OK, so I like to study a lot of political viewpoints, I like the give-and-take of political debate. I like having my opinions challenged in scholarly or friendly discussion.

That's why I am so disappointed in a FB group I joined, and just now left.

It's called The Liberal Library. It is supposed to represent progressive political thinking, but there was a post this morning about how a Wisconsin union has banned Republicans from marching in a Labor Day Parade.