I don't like kicking anyone. In public matches I have created it has happened. I will say that I am never the first to skull anyone. Usually it happens when someone is AFK way too long and the lobby gets trigger happy. I have even left lobbies rather than kick. I go start another even if I left my own.
I would/ we would ask someone joining after a party member got DC'd to leave with an explanation. There should be an in game option to change the match from public to private to help avoid this situation. Its awkward at best.
As for letting someone help carry me through to zone 5 and then kicking them for no other reason than hatefullnes, I see that as just anti-social behavior in my book. I would be afraid to enter a movie theater with anyone I knew like that had gone in there. Some people really have a warped sense of self worth.