I think it's already captured in Crocker's rules definition - "one authorizes other debaters to optimize their messages for information, even when this entails that emotional feelings will be disregarded". It's not about being rude for the sake of being rude - if a kind word provides some context best, a kind word should be used. The idea here is to free your interlocutor from having to constantly censor their communication in order not to accidentally offend you.