Nice. So let's see...
Our leaders would have us believe that the risk of getting COVID is reduced by the shot. If that worked perfectly, then people who got the shot are at no risk.
That means that people who didn't get the shot are the only ones at risk. In that case, it makes sense that the cruises want them to have insurance to mitigate their own risk. (I wonder if it's legal that they mandate insurance for a subset of the passengers).
At this point most people in the U.S. have either received their vaccination shot or have been exposed to the virus. Many people have both, which includes me. The risk now is very low for infection and getting lower every day. Again if one is vaccinated their is very little risk of sickness.