Who knows with Xavier? All you have to do is set him up to have a "mysterious look" in a comic and you're all set for future retcons. "No, it turns out my villainous brother Cain was not attempting to go about bettering himself but, rather, when he was imprisoned by Onslaught I changed his outlook. It was a corrupt use of my abilities but I'm sure eventually all will forgive me because I am...Professor Xavier!" or "True, that little girl would have enjoyed her bubblegum ice-cream more than I would have but I was really in the mood for it; thus she was not generous it was a corrupt use of my power...but knowing I saved the girl from obesity - and got punishe by the fact that those bits of bubblegum are only big enough to get stringy and stuck between your teeth - you will forgive me because I am...Professor Xavier!"

He's like the X-Men's version of Chuck Austen and Reginald Hudlin backed by Quesada rolled into one - continuity be damned, we got Xavier to justify anything we write.