But I view non-humans as aliens. Even beyond the physical distinctions, they shouldn't see the world the same way.
How many players can successfully, and continuously, play non-humans as aliens? Heck, how many players can successfully and continuously play a
human from a medieval fantasy world, with no modern sensibilities thrown in? From things I've read, the races that
are very alien are generally disliked for that alien nature. For example, kenku are often thought of as a pain to play because they can only mimic, and lizardfolk are often seen as boring, emotionless cannibals.
Also, on a typical fantasy world, most these races are from the same planet, or even the same part of the same planet, with fairly frequent contact with each other, can easily learn each other's languages, and can even interbreed with each other. They're less like different species of alien and more like different breeds of dog or cat. There's personality and physical differences between different breeds, sometimes even very strong differences, but when you get down to it, they're dogs or cats (and no, humans aren't the ur-species in this example; they're just another breed).
You want there to be differences between humans and non-humans? Then write up a cultural cheat-sheet for each race and hand it to the players. But I'd bet that none of the cultural differences you come up with can be expressed by +2/+1.