For what it's worth, I think that involuntary quarantine of people solely for having infectious diseases is a bad idea and violates constitutional due process to boot. We haven't done it for decades and that doesn't seem to have caused a problem. I do view holding people responsible for damages caused by not voluntarily quarantining themselves as perhaps ethically acceptable.

Quarantining of people at immigration is legally supportable, of course, just as customs inspections are.