Because its a paradox. You're discriminating against those who discriminate.

Simply put we must first eliminate the root cause, ignorance. Until people realize that intentional stupidity is not a good thing, nothing will change. Yet another reason why stupid people shouldn't be allowed to breed.

Beacause its what comes with mixing all kinds of different cultures and beliefs.

Because discrimination is as much a part of human nature as is jealousy. Can you imagine trying to eradicate jealousy from existance? It's not going to happen. It's a negative human emotion or instinct and it will not go away. I think discrimination is even more prevalant lately because it has been made into such a big thing.

Simple answer: America is not made up of the same people. Where there is diversity there is going to be discrimination. In fact, if we were to ALL be the same ethnicity, religion, and sexual orientation, there still would be discrimination. Humans are wired like that. I am going to copy and paste from another answer explaining about why we discriminate: "Why can't humans agree to live and let live, why must someone always be right? http://www.answerbag.com/a_view/5376571 The human animal is wired that way. Instinct and nature says that we must compete to survive which is, actually, not a bad thing. The problem is how it manifests when all natural non-human competitors are removed. We do not have to fight other species to survive. The only creatures we are fighting, at least in America, are other humans. In other places it is wars... between humans. We have a natural need to rise to the top of the food chain and it is b*stardized into stomping on the rights of other humans. By being "right" all the time it is easier to stomp on the rights of others. This means that for a good chunk of us we "have" to be "better" than others or always "right." I do not need to be better than others and I do not need to be right. Luckily not everyone does need to be better than others and always right. I find those people much easier to get along with.

Because people are human. Even animals discriminate. If you tie a ribbon on the neck of one sea gull, the others will peck him to death. People, like animals, are threatened by differences.