That's the problem. The concept of what is reasonable is too nebulous to rely on.
Also people are quite simply really dumb. You can make some innocuous statement like "others have found nasal rinses to be beneficial", and some idiot will get themselves hospitalized with a draining abscess in their face. It turns out that person decided their nasal rinse was going to be alternating eucalyptus oil and bone broth because someone on Facebook said that was the most healing, and they claim that you as their doctor said it was OK. The case gets escalated to you having to explain to the board that you didn't make any such claim, but because there is a record of you saying that nasal rinses can be beneficial, it can be at the discretion of a "reasonable person" if that skirted too close to their line of culpability for the injury that the person sustained.
The solution is to stick close to what is accepted medicine, and if people want to complain about establishment medicine, then let them. Doctors understand there is safety in the herd.