That's a majority of the worlds' scientists, teachers, politicians, and just about every profession.
So even assuming you are arguing in good faith, an anti-vaxxer and/or a flat-earther are people who can be shown irrefutable evidence that goes against their beliefs and they will simply close their eyes, plug their ears, and scream and shout until you go away. The opinions of those people are ones I don’t care about or think worthwhile because they have already made up their minds and are working backwards to look for evidence that supports their beliefs, and invalidating all others.
Dismissing one’s ideas based on group membership is a terrible strategy for truth-seeking. It’s a root of all kinds of problems we see with team-based politics where both sides have turned their brain off and largely accept the entire slate of talking points their side serves up.
It also borders on the definition of bigotry.
I would trust very ñittle he had to say about things outside of his direct experience, since his BS detector was apparently broken, but I would tend to trust his knowledge of things he had dealt with directly.
While I don't judge people for their ideological bent, I do judge them for uncritically accepting BS because it fits their ideological bent. This leads me to dismiss many of the knowledge and opinions of people who find themselves trapped in the ideological games played by our media.