I wonder if the numbers could back that up? Like the cost of treatment of an unvaccinated child getting a preventable disease, versus a vaccinated child getting the same disease? Also, the number of children in each group? No vaccine is 100% after all.
There could be an actual cost to the healthcare system for choosing to not vaccinate. If that's the case, creating an incentive like a tax credit for vaccinating could be an effective way of reducing cost overall.
I'd like to see someone study this, if they haven't already.