While it is lore supported that Rogue Guardians exist (see Ghost Fragment: City Age) it is also supported they are hunted down with extreme prejudice akin to that of the Ahamkara. Current factions allowed access to the Tower are monitored by the Vanguard. Any philosophy that encourages in-fighting is exiled and all Guardians associated are "encouraged" to "realign". I wouldn't mind hunting down Rogue Guardians in a PvE situation but the current tone of the game is to support unity and cooperation. Even the Crucible is designed more as a War Game Simulator to promote Esprit De Corps rather then animosity. It would not support open world PvP.