I'm not a US citizen, but you might find that most US citizens would prefer their government to prioritize the interests of US citizens over foreign nationals. Just as I would expect my home country's government to prioritize the interests of its citizens over foreigners.

> interests of US citizens

The people who own businesses are US citizens.

There are a lot more US workers than there are US business owners.

> Why?

AFAICT, the parent answered that with "This whole system...puts U.S. citizens out of work." (Whether that's actually true or not, I'm not entirely certain, but the argument could definitely be made, and, in all likelihood, convincingly.)

> What business do you or I have in forcing upon them what they can do? any more than they would have any business forcing themselves upon us?

Presumably, it's people's business because the US is basically a nation governed by the people who see it as their responsibility to help ensure their basic values (peace, prosperity, life, freedom, justice, pursuit of happiness, etc.). So, when there's regulation that affects the people, it actually is their business.

> "This whole system...puts U.S. citizens out of work." (Whether that's actually true or not, I'm not entirely certain, but the argument could definitely be made, and, in all likelihood, convincingly.)

If bringing people from outside the USA into the USA puts people out of work, doesn't having children also put people out of work?

> What business do you or I have in forcing upon them what they can do?

It's called regulation and we do it all the time.