Certainly agree that testing positive would be a monumental disappointment and would spoil an expensive vacation. But not knowing you are positive and not being postive are not the same thing.
As disappointed as I would be to learn I was positive, I would feel worse learning that I was the anonymous vector spreading the virus to other passengers. And I wouldn't particularly appreciate another passenger (unintentionally, of course) spreading it to me, because "they didn't know".
While most people have very mild symtoms these days, there are still many who have complications - hospitalizations are again on a pretty steep rise lately.
It is frustrating and complex, with no easy solutions. A little spit in the morning? Well, to coin a phrase, spit happens. 🙂