There's a lot of room between 95% effective and useless. From everything I've read the vaccines are still a significant help, especially for preventing severe cases, even if they are less effective than against previous waves.
Would be interesting to know if/to what extent it prevents transmission. Assuming the booster reduced severity, but not transmission, it would make little sense to require it, since there is little/no negative externalities by someone not getting it.
One of the potential negative externalities is overwhelming hospitals, pushing out others in need of help.
This line of thinking could be extended to banning junk food, motorcycles, cars, etc.. Where do you draw the line?
Being in the hospital is a negative externality in a world where health care is delivered by humans with a lot of long training.