It wasn't "legal status". It was "subject to laws of the country" (i.e, excluding diplomats).

If the very constitution of the country classifies tourists as "not subject to the law of the US", that's some The Purge level popcorn. All visitors and illegal aliens would have had diplomatic immunity.

The US can amend the constitution. It has not. SCOTUS has no legal right to do it unilaterally.