Just to add a tad, the number needed for herd immunity differs by disease. For polio, you only need to get around 80 - 85% of the population immune before everyone is effectively protected. For measles, on the other hand, you have to get to 95%. That's one of the reasons polio is expected to be eradicated before measles, every % point higher is harder to get, so 95 is a tough goal to reach.

I was thinking that we need a stronger term than idiot, but it occurs to me that this behavior is actually criminal. It causes grievous harm to one's society, which is the criterion for criminal behavior. Therefore if social pressure is not sufficient to correct this behavior, legal means will need to be employed.