User blog comment:VeXen/What's wrong with this world?/@comment-4651179-20120213225954

Doctor Doom joined the FF in a secret pact with Valeria, also, in exchange, Reed helped Doom to regain his intellect...

Magneto wanted redemption, that's all I know... But still there are other great X-Men villains alive or in the bad side: Mr. Sinister, Arcade, Sabretooth, Hellfire Club with the Sentinels.. etc