Well, if herd immunity is a useful 'thing', then why not make use of it's alleged benefits? It is surely an unwise action to risk vaccine injury to protect against an illness that you are already safe from due to 'herd immunity'.
I suggest reading about the history of the development of the polio vaccines - Maurice Hilleman made clear that it is likely that the process caused a cancer epidemic that we are experiencing now and also may have been responsible for bringing HIV to America.