An alternative not on your list: immigrants aspiring towards assimilation into a single culture to which they give their allegiance, superseding their original one, of which nothing remains but the dressing-up aspects.
"let the problem solve itself"..
How do you have a policy of people just voluntarily doing what is most convenient? Can you eliminate crime that way?
ETA:
incoherent
All I can see is you stating that MC construed in a particular way has consequences you don't like. That isn't incoherence
"let the problem solve itself"..
I'm not familiar with the history of the migrations to the USA of the 19th and early 20th centuries beyond a quick look at Wikipedia, but from that, it looks like it pretty much did solve itself. There was friction. It passed.
Can you eliminate crime that way?
What has that to do with this discussion?
Here's the new thread for posting quotes, with the usual rules: