People often mock what they fear, or what they don't understand. For some, it also makes them feel superior, to make fun of someone (or something) that they view as a weakness. Usually, however, it really has more to do with their OWN insecurities, than the person or thing they're making fun of.
The more exposure people have to something that is unfamiliar to them, the more they understand, and the less they fear. That's been true about many cultures and sub-cultures in our nation's (and our world's) history. Which is why, in my opinion, "middle America" is sometimes predisposed to being xenophobic and intolerant, because they're so insular. In the major cities lining the east and west coasts, you typically find people to be more tolerant of people different from themselves, because they come into more contact with people that are different. This isn't ALWAYS the case, of course, but I'd say it's fairly typical.
