This is how denialism works. Things that have been accepted as reality by non-denialists are rejected by others. So you have vaccine denialists, evolution denialists, Holocaust denialists, HIV denialists, moon-landing denialists. They typically use logical fallacies and almost never operate in good faith.

Also, vaccines have basically been a victim of their own success. It’s easy to look around at a healthy population and think that the thing preventing many now rare diseases didn’t really have anything to do with it. I’m surprised someone as old as Bobby Brainworm falls for this, but humans are fantastic at not learning anything from history and not listening to wiser elders. Humans are also great at not understanding science.

The anti-vaccine thing is very much akin to the anti-government thing. The idiots that are still cheering on Republicans and the conservative ideology as they break government norms and government services and institutions have no idea what government was doing for them, but like the measles outbreaks and the anti-vaxxer idiocy, we are all about to find out.