Mandatory Vaccinations

Vaccines are well understood. There's no question of whether they work - time and time again, evidence has shown that vaccines are effective in preventing disease.
You have to travel as far as Wikipedia to find overwhelming amounts of evidence - for example, http://en.wikipedia.org/wiki/MMR_vaccine - numbers that demonstrate the power of the vaccine. (and if you read long enough, you'll find some more fun evidence that people have died because of the autism scare, which is truly frightening

The same can be said for the opposite side of the argument. The fact is that studies, polls, ect. can be manipulated to produce what ever results are desired. If you look long and hard enough you can find just about anything on the internet to support your claims, but that can be said for both sides.