Even if every single passenger and crew member is fully vaccinated cruise ships are floating petri dishes anyway. My mother was on a cruise in the 60’s where there was an outbreak of some flu-like virus and at least 4 passengers, mostly elderly, died. That was enough to put me off cruises for a lifetime.
And still masking up for the cruise outside the cabin?
Not to mention those pesky Legionnaires breakouts, of decades ago. That did it, for us.
And, having to be stuck on a floating Petri dish, for days/weeks, seeing the same people at every meal.
Just not an appetizing lifestyle, for us. Others can certainly have at. Shot Passports, and all.