The problem is that for many vaccinations your child doesn't need them if all the other children have had them. So - you can be selfish and protect your own child and let the others take whatever negative consequences (if any) of the vaccinations.

So - in order to be fair, the govt insists that all children be vacinated. Otherwise it wouldn't be fair to ask a parent to decide between exposing their own child to some risk (however small) or to expose other children.