Maybe the "Knights of Ren" are the equivalent of the old-EU "Imperial Knights" or the Sith as presented in the 1974 rough draft: basically Jedi who are loyal to the Empire (and thus technically villains), but who don't use the Force for evil stuff like trying to conquer the galaxy at large.
In other words, rpvee may be right in suggesting that Kylo Ren is the worst of a not-quite-so-bad bunch.