Why I don't like Non-Human Character Races

Invariably, when I start a new campaign, someone will approach me and ask if it's ok to play a non-standard race/type. I will patiently listen to the player, and try to divine his true motive for making such a request. It always boils down to one of two reasons.

1. I just read this great book/saw this great movie, and I really want to be like this character. (Fan-boy) or
2. I'm really looking for some kind of edge, some advantage that will make me better than everyone else (Wonder-girl.... kind of a private joke, I'm thinking more of bad for you, even though it tastes good, Wonder bread than any kind of super-hero)

I'll listen, and then tell Fan-boy or Wonder-girl "Sorry, that character doesn't fit what I want to do." I'll then try to suggest what niches need to filled in the party.

One reason is that Fan-boy probably has a short attention span. Once his current obsession starts to fade... He'll have a new one, and want to change characters. And Wonder-girl isn't going to be happy with a lopsided character. She'll be happy with the pluses, but grouse about the negatives and want to "forget" they exist.

But, the main reason is that we are human... And we think like humans. It's hard roleplay, convincingly, another race. We have a tendency to treat Elves, Dwarves, and Halflings as differently shaped humans. We may make the dwarf grumpy, or the elf flighty... but we still run them as human. They should have very different outlooks on life, different social conventions, and approach obstacles in very different ways. Dwarves are very long lived, and elves nigh immortal, their years must lend a different perspective. A player that pulls this off deserves bonus points and should be commended. If it is so difficult to play these races correctly, who are at least somewhat close to human, how is it possible to play a non-humanoid character?

One more thought for Wonder-girl. Heroes are those that overcome adversity... not the ones who overwhelm it.