I'm with the Nauseating Cliche Police.
There's a huge difference between playing a character that follows one of the usual personality archetypes and one who has that one-in-a-million "rebel from an evil empire" syndrome. Stylistic reasons aside, there are good balance reasons to disallow this sort of thing; many of those Evil races are more powerful than their Good counterparts, as a balance factor. So, the "Good Demon" usually wants all the advantages of a powerful race without the roleplaying penalties the race comes with.
Sure, being an outsider makes a nice plot hook, but it's just staggeringly overdone. The Drizzt Syndrome isn't the only cliche I get tired of. How many characters have you played with who was the sole survivor of some cataclysm that destroyed their hometown? Maybe it was overrun by Orcs, maybe it was a divine thing, who knows. How many watched their parents killed by (bad guy/monster race/wild animals/a Flumph)? How many drink a lot, sleep around, fight every Evil thing that moves, and spend all their remaining money on better weapons and armor?
Just for kicks, I played a sane character once. He came from a loving middle-class family, his parents and siblings were all still alive and were happy to see him when he returned home, and he had a steady girlfriend. He didn't have any big traumatic experiences in his past.
He went into adventuring to raise enough money to start his own business, and once he got it he more or less retired (well, the near-TPK in the Abyss along the way helped that one a bit- the one time he ever did an adventure for the Greater Good). He wouldn't fight Evil things unless he had a good reason, and he didn't like the stupid "you only live once" risks most adventurers thrived on.
It drove the rest of the party nuts. They were so used to the hack-n-slash mentality that when someone said "err, no, I don't want to kill that Red Dragon, he hasn't done anything to ME, and those things can hurt" they got confused.