often asymptomatic illness
Surely that's part of why vaccinating against it is so important? People are not aware that a child has it, the child comes into a contact with an unprotected pregnant woman, and bang, the baby gets CRS.
Personally, I think it's extremely selfish not to vaccinate your child against rubella, as well as short-sighted. But then, I spent a large chunk of my early life living in countries where most of the population enjoyed Medieval levels of health care. So I saw people with smallpox scars, living with the after-effects of polio, and suffering from active TB. The direct consequence of these object lessons is that all my DC have a full vaccination record, including the one who reacted badly to her first dose of whooping cough vaccine: she just got the alternative vaccine at a year instead, and I was nightly glad of herd immunity in the interim.