You just don't let anyone into the US. Even I couldn't live there unless I basically invested a whole shitload of money into some businesses there.
Likewise with you. You just can't live here without jumping through some process.
As for Mexicans I never agreed with open borders - here or in the US. Frankly I couldn't believe that the Democrats just ignored your laws and let them flood on in and didn't even deport them until it became out of control and too hard to tackle with millions in. Madness.
However as it happens with white South Africans the countries that should have let them back in before it went to shit were 1. The Netherlands and 2. Great Britain - depending on heritage. I however have zero problem with white South Africans resettling in Australia. They are a similar culture to any other first world country and would assimilate just fine.
The other thing I can't believe about Mexican immigration and the democrats is the democrats are supposed to be all about social justice etc... but part of the reason they were allowed to live in the US illegally was "cheap labour". It may not be slavery as such but you'd think you'd have learnt about the downside of cheap labour from foreign countries after slavery. You get left with an entirely different demographic that causes trouble and a large hangover for centuries afterwards.