I'm really conflicted on the issue of opting out of childhood vaccination; while I strongly believe in personal autonomy (and by extension, the right of a parent to make decisions for their child), I also think that those who refuse to vaccinate are expecting the rest of society to assume the risk (if any), while they avoid the risk but still reap the benefits. This seems selfish to me. I'm not sure what percentage of the population declining vaccination will result in a significant increase in the diseases the vaccines prevent.