There is a difference between the US enforcing visas within the borders of the country and the EU using their laws to affect an American website, allow slurping up data of Americans living in America outside of the EU's jurisduction. America already went to war to stop Europe from ruling over us. The legality of operating every jurisdiction is going to be more complicated due to having to deal with unreasonable demands of foriegn countries or contradicting laws. It's much more complicated than a country enforcing who can be within their borders with visas where the US has clear jurisdiction. If you were to ask me if I think X should respect US law like the DMCA I would say they should absolutely be following US law.

The enforcement is the problem if it is not secure legally. If you want to handle it with an iron fist like a dictatorship sure you can create laws to that effect, but there should be some human values on the books that makes those laws humane.

Considering practically every concept has the concept of a temporary visas, it must not be that insane of a concept.

It's basically an objective fact at this point that excessive immigration is really, really bad, just look at all the politicians flipping sides on the issue. Look at the stats on European countries with the highest immigration rates vs those with the lowest (e.g. Poland)