I fail to see the sense in this, myself. I think the child and his parents bear the full responsibility of whatever happens as long as the school staff can respond like adults in the unlikely event of an emergency. This condition should have no other impact on the rest of the student body nor on the school. The boy and the family can then decide if those "risks" are something with which they can cope.
It should not be necessary for everyone to take care of everyone else, outside normal limits of ordinary civility.
That sounds good in theory, but in the real world of today, is not what will happen. If he gets sick or dies, the parents WILL blame the school and sue them.
If you agree to punish an entire school for one kids allergy you’re not seeing any sort of bigger picture.
The school is correct in banning this kid. End of story.