What I mean by diversity is immigrants bringing different racial groups, ethnicities, cultures, religions, languages, dialects, foods, customs, etc., and then I said in the OP why people may fear diversity.
One reason people fear diverse groups is that they disrupt homogeneity and not assimilating, which kind of sounds what you're talking about.
I would say that all immigration waves change America or at least their communities is some way. You can see it the restaurants, types of businesses, places of worship, etc. Eventually they do assimilate, especially the kids, the grandkids, etc. It takes time.
...I have been to Chinatown in NYC, and it feels and looks like a foreign country. I don't even know if the people can speak English or if they just live in Chinatown and not assimilate. It seems possible to me though. What do you think about places like that? Is it really a threat?
Hm. Fear is a bad word. Worry is better.
Lack of common identity decreases social trust, and with it, the community necessary to sustain a whole host of things we like, from little leagues to charities to public benefit programs, to peaceful representative government.
Liberals score high on "opennes to new experiences" - as a conservative I often feel that Liberals see only the wonders and fun of new experiences when they look at diversity, and never the flip side of that coin. A diverse society will feature the ability to celebrate St Patricks' Day, Cinco de Mayo, and Chinese New Year. It will also feature groups like the KKK, La Raza, and Black Panthers.
Unless we are willing to assertively stake out a national identity and declare that to be the mold to which we shall all bend, diversity will bring with it problems. That doesn't mean we should force immigrants to match the current ethnic make-up, but it does mean that we should mitigate the troubles they can bring by pro-actively assimilating them into broader American society.
It's a balancing act. The more new people's we bring in, the more proactive we have to be in assimilating them. The less active or successful we are in assimilating them, the less tolerance there will be for bringing new people's in.
One anecdotal example. After college, two of my friends and I moved into a condo in a low-rent part of town (we were still broke waiters and booksellers). We were the only white kids in about a square mile, the rest was all hispanic. Most were probably varying shades of legality, but we thought it was cool because, bloc parties and great mexican food at the nearby restaurants. One of my buddies had a classic mustang he had rebuilt with his dad - beautiful car. He's pulling out to work one day and one of our neighbors T-Bones him, doing about 35, which isn't terribly fast, until it's coming out of a parking lot, and it hits you in the side. The other driver then pulled back, and drove off. Naturally, we called the cops. They came and took notes and then asked if we knew anything about the guy, a tag number, etc.
"Oh yes" we replied, naively, "he lives in that apartment section right there, and works at [Restaurant name] down the road - he's probably there now on shift, and will be back tonight."
The two cops look at each other. "Er, is he an illegal?"
"Uh, I think so - why?"
And that is when we found out that the regular law that applies to you and me doesn't apply to illegals. Because it's too much trouble and paperwork, so long as they aren't actually physically attacking anyone, the cops were under direction not to ticket them, not to arrest them, not to take them in, not to do anything that would force them to notice that the people they were interacting with were here illegally. Tough luck, kid, you understand, I'm sorry, but there's nothing we can do - you'll just have to fix the car.
We were all pretty libertarian at that point; more people meant more workers and producers and innovators and thinkers, etc. so on and so forth. After that, we all looked at our neighbors in a different light. We went from thinking we were the local pet-gringo's who liked to drink beer to viewing ourselves as surrounded by law breakers who could do as they pleased.... because they could. Community was broken. My buddy tried to confront the guy and get him to pay for the damages, but that went south pretty fast, and we left after being threatened. We slept with loaded weapons next to our beds after that until the lease was up.
We came face to face with the fact that those around us hadn't assimilated to our system of Rule of Law, and the result was that not only did our tolerance for them go down, but our fear went up, and our perception of the likelihood of violence (which can become a self-fulfilling prophecy, over time) increased dramatically as well.
