The capitulation system of Civilization IV was the worst system of that game, which says a lot because it was competing for espionage for that title.
Because the most annoying thing in CivIV was declaring war as a group against a civilization and the war ending because someone capped the civilization. Voluntary capitulation is fine, and liberation capitulation is fine. Though, personally, liberation capitulation should liberate the territory as a gigantic city-state as opposed to a return of the civilization.
I don't like perma "you-smack-them-once-at-the-border-and-they-cap" capitulation.