You're trying to draw an irrelevant conclusion, and you're not going to get far. While it is a fact that people naturally posess behaviors of ingrouping bias and frequently construct social stereotypes.
Blatant racism on the other hand - which is the topic of discussion - is a much different matter. While you have correctly pointed out that most people make spot judgments on others based on physical attributes, racism is a social construct - supported by memebers in society - that seeks to place rank on individuals based on these perceived distinctions.
From this system of rank, oppression begins. This is racism, and this is what is being discussed, and this is what I'm opposed to. You don't have to be in college to not have your head in your ass. If you want to contribute, I suggest you take yours out if you want to be taken seriously.
Anyway, rank could be anything. In this situation, the rank of "citizen" is being denied - primarily from people of Mexican descent. Now, I'm not debating views on immigration, as mine are rather non-mainstream and probably wouldn't have much support here. What I am discussing is the effectiveness of politicians in manipulating middle Americans into voting a way that benefits the politicians instead of the voters.
The arguments made for "tightening the border" are marginal, at best.
One which I will tackle now is hwo national security is repeatedly brought up; that the border is a method for potential terrorists to "infiltrate" our country and wreak havoc on the nation. Yet the politicians who are making this claim do little to prevent much higher risk threat, like container ships with nuclear weapons, access to materials for destructive weapons, or mention at all the exact same "risk" that exists with our much larger, much more porous border to the north with Canada (who actually has terrorists, as of late).
What really gives here? Well, it turns out, if you didn't know, that a lot of middle America is pretty intolerant to non-white non-American people who look/smell/think/dance differently than them. Now, the people in charge of this country, who are essentially very smart businessmen despite the clergy they drive to appear as, know exactly how to capitalize on this. By trying to invent marginal at best issues (others including flag-burning, terminal euthenasia, and last elections big winner: gay marraige) to appeal to middle America, they draw middle America to their side. In the case of immigration and gay marraige, they appeal to the intolerant racist views prevelant throughout middle America. With flag-burning and war, they appeal to blind patriotism (see: nationalism).
What's the point in rounding up all of these votes? Well to win, obviously. And once in power, it's to execute important, not-so-public legislation that greatly benefits business. And that's capitalism. America used to be what's called a mixed economy (remember high school economics?), but is now, by far, the worlds most capitalistic economy. Obviously, it's not doing to well for everyone, but working quite nicely for a select few. This however, is another topic....