There is still a risk of it happening, and since there IS one, you cannot justify forcing someone else to take a health risk, no matter how small YOU think it is.
I honestly don’t give a lick what Roald Dahl or any other celebrity or famous person thinks about vaccines. If someone wants to vaccinate, let them. If they don’t, then don’t. If a municipality passes laws that preclude unvaccinated from entering public facilities, like schools, I have no problem with that, as long as there are alternatives, like homeschooling.
For the most part, I am against the government forcing anyone to do anything. However, in the case of a major public health threat, I make an exception. I’m against the Gardisil vaccine, because the disease is not readily transmissible just by being in close proximity. When it comes to measles, polio, etc., that is different.