I've only seen some of the movies, so forgive me if my understanding of the story is wrong.

That being said, I think it's a little harsh to call Xavier a sellout. He's providing shelter and education to young people who've been kicked out of their homes, who probably wouldn't survive for long on their own. The fact he's managed to make it financially solvent should be seen as laudable. And... more than that, Magneto wouldn't be able to cultivate members for his own movement without Xavier doing this! They're really not diametric opposites, so much as mutually dependent.