You seem to be from the USA when you say "migrants could very well start a civil war here in America"
Do you realise that the USA is a country made up of migrants (free settlers & slaves) and that its economic engine , namely Silicon Valley , has relied heavily on immigrants to provide the skills and management of today's US economic power hub. Californian farming wouldn't be economically viable without cheap immigrant labour mostly ex Mexico. And that's California alone!
The US economy is morphing into a consumer economy as its manufacturing declines so from a macro economic view, the more consumers the merrier.
The US already prints/generates $2 Trillion P/A out of thin air without the corresponding productive economic activity so the bigger the tax base (if only VAT) then the better.
Of course if your argument is racist, then that's another issue which I wouldn't want to contribute to because that's too animalistic for me
