>By "political correctness" people often mean "the basic requirement to treat your fellow humans respectfully", and that's an incredibly low bar.

I've gotta disagree. By "political correctness" people generally mean to not saying or doing anything that could be perceived as offensive. Especially against collectives perceived to be vulnerable.

For example, in the tiny paragraph above I've absolutely respected my fellow humans, but it can be considered offensive because you can suppose I might be looking to justify prejudiced attitudes.

For an even more evident example, political correctness has to do with the political climate and identity (as you mention: sexism, racism, homophobia, transphobia, or anything else, as well as referring to "those groups"). That is very much detached from treating fellow humans respectfully.