Not sure about the legal validity here, but you can be sure somebody would find time and energy to take this to court. I don't think however, that any court would rule to swifty declare this illegal and then be deemed somewhat responsible for the consequences.
History shows that whenever you ask "what kind of jackass would do this?", a number of such jackasses tend to present themselves.
Don't underestimate contrarianism and people's willingness to fight tooth and nail for what they believe in, no matter how ridiculous it may seem to you.
Someone who is prosecuted for violating this will fight it, as they will have the most firm standing.
This sounds like exactly the kind of thing ACLU would fight. And their twitter suggests they will:
That is related to people coming off cruise ships being quarantined, where they are actually confined. This order is different, because you are still allowed to leave your house for essentials, exercise, etc. Not saying whether it's legal/illegal/good/bad/whatever. Just noting that it's a different scenario.
Re:Stay home except for essential needs
by SomeHacker44 on Monday March 16, 2020 @06:09PM
(#22598586)
Even if it is ruled unconstitutional, it could take a very long time to happen, and in the meantime, the effect could be beneficial to society.
Look at how long it took the Japanese internment from WWII to be ruled upon - and that was by modern standards not remotely beneficial to society.
This is a completely reasonable order given the emergency situation. No reasonable person should object to it.
(I did not downvote you)