I kind of share your perspective, but to be honest, my theory about the appeal of the communities you're referencing is that people are not in control over their care, so they do what they can to achieve it. They're stripped of it by medical regulation and lack of choice over who to go to. So they're forced to go to some alternative, totally outside the system, to get any kind of traction in personal autonomy.

The choice, at least in the US, is (1) traditional, science-based medicine delivered in an oppressively regulated system, full of monopolies, regulatory capture, patriarchical, patronizing attitudes, and restrictions on how you care for yourself, or (2) untested, unscientific, but free approaches to care where you are the active driver. This is a bit of an oversimplification, but not much.

It's absolutely no surprise to me that we have so many problems with lack of engagement in preventative self-care when the entire system revolves around deference to authority. Your question "should you trust an authority?" is a bit misguided, because in the end, if you say no, what choices do you have?

Expertise in the medical system is based on hoop-jumping and guilds as much as actual rigor of argument and expertise.