Knowing that the vaccine doesn't prevent the person from getting and spreading covid. Knowing that the point of the vaccine is to prevent serious illness in the person receiving it. I struggle to understand why you would not even question how important they are in that setting unless you are worried they have dropped that extra safety component.
It's part of the reason that bed capacity has been so difficult to keep constant or increase.
Vaccines reduce the risk of spreading the virus. People who are vaccinated are less likely to get seriously ill. This absolutely doesn't mean you won't die if you are vaccinated. Think seat belts in car accidents. It is all about reducing risk. On mass, at population levels, this means ICU have capacity to take in other seriously ill people. If ICUs are full and there is a plane crash or whatever where many people are seriously injured we are screwed.
You could make the point that increasing the spread when everyone is protected is fine but that allows for increased mutations.