But the constitution is not worded as if they don't have the same fundamental rights. Even in other countries, it is the same; this is done to prevent slavery and unjust incarcelation. So visitors have the same fundamental rights to free speech, fair trial, etc.
The US has also agreed to international conventions. But the current administration seems to not care
It's definitely not as simple as you're making out. Political speech aside, visas have routinely been cancelled without forewarning for all sorts of reasons historically.
Does someone on a short term visa have the protected right to purchase firearms? Visitors aren't even permitted to get a job without the appropriate type of visa. Being allowed to work is a pretty fundamental right.
I expect there's a difference between the bill of rights and the constitution, and likely further nuance as well.
