The problem here is that not all diseases are the same in terms of risk to health/life or even the ability to infect others. Comparing Smallpox to Polio to the Measles in equal terms is a stretch at best and probably closer to being dishonest. Many people recognize that either wittingly or unwittingly and so getting vaccinated against Measles and Chicken Pox just isn't a high priority. Now to talk about the MMR vaccine: It has had a rough go the last few decades. It was reformulated a couple decades or so ago and the efficacy was massively reduced to around 30% or less if I remember correctly. They went back to the old formulation later but not after a full decade or more of using the new formula that didn't really work. In several of the measles outbreaks of the last decade or so - most, if not all, of those that got the measles had been vaccinated. Of course then everybody blames the anti-vaxers for the outbreaks :(