Targeting American citizens just because they came from New York (or New Jersey, Connecticut, Louisiana or wherever) is a blatant violation of the Fourth Amendment. And I suggest the reason so many forum members support it is because they aren't subject to it. How about if Florida started to do what China did. Go door-to-door and take people's temperatures. And if you have an elevated temperature from a cold or other minor illness, be forcibly taken from your home and quarantined. Use the same arguments in this topic to justify or refute.
There is a law on the books from the Spanish flu pandemic of about a hundred years ago that empowers the CDC to quarantine areas to prevent disease spread. Read it here:
Legal Authorities for Isolation and Quarantine
| Quarantine | CDC
The governor could declare martial law but probably will not. It would amount to political suicide.