I think that the worst thing about RP is that it is hard to moderate... you know.. people abusing his job, people glitching whit chairs/airboats ... a guy that think it is CSS...
Any game mode that is potentially more fun than others is difficult to moderate one way or another because they all require cooperation, common sense, and obedience from players.
TTT is difficult to moderate for example, as well as Wire Build, and any other game mode that isn't straight forward kill the opposing team.