It is about personal preference, I personally think it would be good to get some form of etiquette going, but those are dreams long gone since changes to the game and people having different views.
The only thing here is to either be polite, courteous and think first (not like I can talk). You can simply use the commands to find out who they are or if in a guild and their username. You can also use a sense of decency to just type "Sorry Full" then kick.
I have never kicked someone out of a game unless they were "AFK" in a 2-4 man group run on Hardcore to save their character from death.
Personal Preference, and even Vicki liked joining my runs and going AFK for personal reasons because her characters never died and gained levels just sitting there...

the good ol days.