I can't belive were taking KH so seriously right now.... lol
Ok.
Well, it really is debatable whether they were evil or not, but as a whole I can't say they were, seeing how they're just that - an
Organization.
Demyx for instance didn't come out with that much of a fighting spirit unless it was to try and bring Roxas back, and the second time around Sora and Donald were gong ho on getting him out of the way so they could save HB; throw in him apparently being insulted by Roxas's "betrayal" and you got him willing to fight.
We've never seen him try to turn anyone into a Heartless and so far weren't really told what he was doing in the Coliseum save for trying to get Roxas back, seeing the instructions Xemnas gave him.
Then we have Xaldin, that while he indeed wanted to simply regain his Heart, was an utter bastard that was out to actively hurt people and put Beast and Belle through hell.
Other good guy examples - Lexeaous, who seemed rather honorable and his attempt at getting Riku was to stop a
rebellion inside the Organization, one which would have possibly led to a much worse conclusion.
Well, Roxas, we can't ignore him. Definately a bonus to the Organization's moral level.
Other evil guys examples - Larxene :\ regardless of anything. She was just a bitch.
Luxord didn't seem to care much about anything in Port Royal.
When it comes down to it, though, whether they were evil or not seems to take second to each and every single one of them being
selfish.
Marluxia did pretty nasty things to Namine and Sora, but who knows if he wouldn't have truly worked out the Organization's ideal and was actually rebelling because he thought Xemnas was lying to them all.
Saix seemed good at using the situation in his advantage, but was also fair enough not to harm people needlessly - he came out as pretty evil, but a calculated one, so I have to credit him for that.
Evil or not, the end result is that they hurt people, and from the protagonist's pov, that made them evil.