I don't think that herd immunity is a myth, but I do think that each individual person's immunity plays a big part in whether they will get sick, not just whether they're exposed to germs. This, to me, is a real argument. It's not strong enough for me to vaccinate though. The reason why is because I don't believe that vaccines are safe and that people who manufacture vaccines are concerned with safety as their number one priority. Also, I think that there are too many corporate/political conflicts of interest. If everything possible were being done to make sure that vaccines are safe, then I would feel that herd immunity is a very important reason to get vaccinated (for some things). Part of the whole "social contract" issue is being able to trust that the vaccines are as safe as possible. That's just not the case.
Doctors get p4p benefits which will push them financially to push vaccines. Vaccine manufacturers are allowed to give undisclosed amounts of money to the CDC and various health associations. They give heavily to the American Academy of Pediatrics. The AAP often sends representatives to speak on behalf of vaccine legislation. Drug and vaccine manufacturers are allowed to pay professors in medical schools (even Harvard) and they're allowed to write textbooks for medical students (clear conflicts of interest there). There are more conflicts of interest, but these are the few that come immediately to mind when I hear about the "social contract" that we're supposed to uphold.
I think that herd immunity is real, but vaccines are not safe. If the conflicts of interest were corrected, I'd feel more comfortable putting myself and my children at risk. Then, it would be a real social contract instead of feeling like my children's bodies are a product to be bought and sold.