The core issue is the common good. Measles travels through the air – and if enough people opt out of vaccinations, they put everyone at a higher risk
I remember having measles as a kid. Believe me, it was no fun. Also, measles could cause birth defects if a pregnant women got infected. If you were elderly, measles could be fatal.
Eventually, after vaccinations became nearly universal in America, measles was declared eliminated from the US in 2000.