It has a lot to do with who we grow up with. If we grow up in an educated multi-ethnic culture, then ethnicity no longer has such a charge. But if we are acculturated in a homogenous group, we will feel more comfortable with people of our same kind. This is the instinctive basis of xenophobia. It is reasonable to be cautious around people whose values are unknown to you, and whose behavior is not predictable.
Xenophobia can be trained in at any stage of life. I have suffered the hate of the Navajo and Apache when living and traveling in Arizona. I understand why they hate the white eyes, because I do too, but I personally do not deserve their bad treatment. Still, I got the bad treatment, and now when I see a tribal member I am on guard. The same thing has happened to me here in Portland. I had always liked and respected every Jew I ever met. Then I was mistreated by an attending Jewish doctor who took offense at me saying the words "a Jew" because in her mind she inserted the word "dirty". That word was not in my mind until she explained to me how offensive it was for me to say "a Jew", and then threatened to flunk me, sanctioned me through the college and required that I take cultural competency training. Other Jews near to me have hurt my feelings since then, and I have developed a reaction to Jews that I did not have before, when I lived in Denver next door to the Ashkenazis and thought they were really decent folk.
In spite of all my education and knowing things, I have feelings that are influenced by what happens to me in my life. Does this make me deplorable?
Oh, and all you decent men out there who think that you are not sexist. If you were born and raised in the U.S. you are sexist. Ask any European, male or female. I am a woman. I have never made anywhere near as much money as my partner, in my opinion because he has a penis. Yesterday I drove a vehicle up to a boat inspection station on the highway and the man with the clipboard came up and started asking questions of a man who got out of the passenger door. At the gas station the attendant speaks to the men first. Men here invariably address men first when approaching a couple. This seems like a tiny offense, but compounded into the reality of daily life, a woman knows that this is still a man's world. Clinton knows it all too well. American men, including educated ones, are unconscious of this kind of sexism "lite". There's no stoning here, but men are not aware of the degree to which they are programmed to be sexist, and should spend more time in introspection around this. I think part of the problem conservatives have with lesbians is the men have no one they can talk to.
I realize I'm making a bunch of generalizations, just like Clinton did. My point is that these base impulses are present in the vast majority of all humanity, and Americans are clearly not above it. Our culture seems to be regressing. In my lifetime I have watched our society and politics become obnoxious. Substantive debate is rare, name calling commonplace. If there is to be a conversation between opposing sides, there must first be respect. Respect is a Universal human need. People denied respect are hostile and possibly subversive.
Liberals in general need to stop denigrating conservatives and dig deep enough into themselves to understand the conservative position. Conservatives need to educate themselves to articulate their concerns and rationales clearly to others. Everyone needs to start with the assumption that the other guys are decent humans just trying to do the right thing, the best way they know how. Then the conversation can begin.