As for being on-topic, the USA is very much a mixed bag. It's hard to do any serious studying about the United States without realizing this, and generalizations poison whatever argument or point you may be making.
That's a good point. There's really no such thing as a "Stereotypical American" since Americans are simply a mix of everything. We were originally Europeans, and then became independent, then allowed people from everywhere in the world to join in and mix it up (of course some groups had a bumpy ride). Even religion in America is ridiculously diverse. Look at Christianity by itself: you have countless groups of varying size who all disagree with each other and who all claim to be right. Yet all of these groups are put under the same umbrella and perceived as the same thing. Tell a catholic that he's the same as a baptist, and I doubt he'll appreciate it. And then, there are many, many, very different catholics. Essentially, there's not just one America. You have northeastern America, which is a polar opposite of mid-western America, and northwestern America which is very different from southeastern America. And even from city to city in these places you'll find great differences. Some communities are almost entirely black, with their own culture, some are almost entirely Latin American with another different culture. Some are so mixed you can't even tell how many cultures are blended in there.
Another note, I think some of these views that people have can be attributed to the "Motivational Sources of Prejudice." Straight from my psychology book: "People are also motivated to view themselves and their groups as superior to other groups. Even trivial group memberships lead people to favor their group over others. A threat to self-image heightens such ingroup favoritism, as does the need to belong." Basically, we're just people falling haplessly into categories that psychologists have studied and identified across many different regions. Most people (not all) feel that their beliefs or groups are right, and that others are wrong. And have you any idea how many different groups and beliefs there are? "Right" is whatever the majority says (but only in a given area of influence), and "wrong" is whatever the minority says. Entirely subjective.