"'all those children are going to get CP anyway so may as well get it when it's convenient' is false, and sets up a fatalistic approach (they have to get it so may as well get it out of the way)"
It is realistic, not fatalistic. They will get it and should get it when young.
"anyone sending their child to a chicken pox party is a selfish fuckwit"
Well you sound lovely 
DS got CP as a baby and immediately passed it to DD who got it two weeks later, so we didn't have to make this decision, but several friends sent their children to play with DD while she was contagious. They are not "fuckwits" and they definitely are not "selfish". From that moment on they treated their children as potentially contagious, which is much better for vulnerable strangers than catching a disease unknowingly.
"Most unvaccinated children will get CP in a country without a vaccination programme. Not all."
Those few are at risk because they will have it much worse as adults.
"if my grandmother had received the shingles vaccine, or if I'd had the chicken pox vaccine, not only would I not have been seriously unwell, but the small baby I was nannying at the time would have been spared the risks associated with the disease"
If your mother sent you to a CP party then none of the above would have happened, either. Given your own experience to the contrary, I don't see why you insist children should be made to avoid CP and leave themselves open to the risk of getting it in adulthood, which is much more dangerous.