I find this fascinating because it's the sort of anthropomorphism that betrays a fundamental understanding of what an LLM is. Language models are not people. You can just achieve the same thing with a fresh context window. The only solid technical reason you'd want a different model is if you find a certain model produces better code and another produces better reviews. Nobody has really tested this, of course.
Not every culture can integrate, not every culture is a step "forward". Also, your examples are quite weak
1. Paganism was not doing too well by the time Christianity became official.
2. Belgium is a joke country (sorry!) that still has a divided population based on the language they speak. Hardly a success case.
3. Americans speaking Spanish also resulted in losing native languages and cultures. It might be okay to accept it, but the implications in your case are obvious, and it definitely would deserve a fair bit of debate whether we're okay with that.
4. Right, because the Reconquista was famously a period of peace and prosperity...
If these are the arguments FOR massive immigration then don't be surprised the vast majority of the public is against it.