Bolded is right. Raiding is "important" to the experience MW brings, but having a favorites list isn't that, its just farming. Use your news feed to farm if you want, but a list of "favorites" wouldn't improve anything. It would destroy the purpose of having rivals.
Why bother looking through your rivals if you could just favorite someone, or an alternate account, just to raid off of. It breaks the rival system, and could be easily manipulated.