I'm not going to take a side on either matter here mainly because none of it concerns me (I did get the MMR before my mom went on temporary hiatus), but I have a legit question:
If the vaccine is as reliable as scientists and experts claim, then anyone who has gotten the vaccine will very likely not get measles, mumps, or rubella. But if the anti-vaccinating people decide not to get it, they'll just be spreading it around themselves and their group. If this is the case, why do the pro-vaccine people even care if they don't get it?
This isn't me trying to defiant. I'm literally curious.
One, as Juncoph said, those people will want be a cost on the system, should they get sick.
That's both treating them during their infection, but also caring for any lingering effects, such as blindness, or brain damage.
Two, there are people who are unable to recieve the MMR vaccine. They may have autoimmune diseases of their own, or have other issues.
These people rely on Herd Immunity. This is when the majority of the population is immune, so the disease doesn't prosper and spread, so they don't catch it.
When there is a large population of people who don't have the vaccine, they are at risk of getting the disease. And they can spread it on to people who CAN'T have the vaccine, even if they wanted it. They put other people at risk, and those they put at risk are the ones most likely to suffer the worst symptoms, or even death.
Three, young babies can't have the vaccine until at a certain age. Until they can have the vaccine themselves they are reliant upon Herd Immunity. The moment a population of un-vaccinated people arrive, their herd immunity is compromised.
Four, it's not ideal to let people risk themselves dying, even if they are happy to. Consider it as the same reason why we insist people wear seatbelts, or we prevent Self Deletes.
Sorry for another large point restating what everyone else has. Didn't realise everyone was writing at the same time.