Refusing to vaccinate a child is dangerous not just for that child but for entire communities. It's precisely this point a colleague of mine was considering when he had the idea that parents who refuse to vaccinate their kids should pay substantially higher health insurance premiums.
Check out this great op-ed piece on CNN.com (link above).
In 2008, one couple from San Diego who decided not to vaccinate their child for measles ended up exposing 839 people, creating 11 new cases of measles and costing their county and state $124,517 (not including private insurer costs).
Even if you set aside the health risks for everyone that children who aren't vaccinated create, reckless parental decisions have real economic consequences as well.