Appearance is something people will always judge on and harshly. My first husband was a dwarf and they're not looked upon kindly in Westeros. He was a good man, though, in spite of being a little too prone to drunkenness, and he was kind to me. His looks did not meet their judgments.

( And, so, if Sansa is a little softer-hearted toward a tiefling because of it, so be it. It's a good thing she learned her manners young. )