just pushes them to double down.

It pushes them out of communities. You’re not really understanding the strategy here. The point is not to make them believe, it is to silence their ideas with a bit of social conformity. This is the same reason you kick nazis out of your bar before they start bringing their friends.

If you make life difficult for people with obscenely bad ideas, you encourage them to either stop or at least be quiet about it. That quiet inhibits spread. It creates new taboos that people are afraid to cross.

Regardless, saying to your loved one "Okay you don’t trust the scientists, but you do trust me, […]

Their loved ones are welcome to do this. They should, actually. I can’t really help them do that, though.