I disagree with that part. The American culture has always been a mixture of other cultures, with our own personal flavor. The entire idea of being a melting pot is perfectly fine, as long as you don't hold to any specific point in time as the One True American Way.
People don't like change. They don't like when something is different than what they are used to. I still wonder how we got from the 80's (my favorite time period) to now. Just as I stare at the kids who wear too large clothes. But, I don't think I have the right to ever say they are ruining our culture any more than my grandparents have the right to tell me the same thing. Culture, like language, is a fluid and mobile thing, changing with the ebbs and flow of history.
Zero Tolerance could be considered one attempt at trying to regain control. The entire idea of going back to the "moral" days as my grandmother used to tell me. Yeah, it could be, but it wasn't that long ago when kids brought rifles to school and most people owned or carried a knife. Is that the good old days?
Life changes, the hard part is letting it go.
Yes, it is true that cultures change. However there is a difference between natural, organic change (from generation to generation) and the wholesale wanton, deliberate, destruction of a people through replacement migration, violating their rights of freedom of association vis a vis their children, their housing arrangements and employment.