I don't think having a Keyblade determines your side. Keyblade wielders can be good or evil (i.e. Sora as opposed to Riku in KH1 or Xehanort as opposed to Ventus in Birth By Sleep). Just considered a faction as a Keyblade wielder rather than a Wayward Travel (like Cloud or Auron). I think that's how it's working, at least.