It's my understanding that there is no vaccine against chicken pox, and the greater severity of it in adulthood (and consequent wisdom of deliberately exposing

It's my understanding that there is no vaccine against chicken pox, and the greater severity of it in adulthood (and consequent wisdom of deliberately exposing children) is understood by many in the, ah, "pro-vax" community. So it's not really an anti-vaccine argument that people do this.