I've also found that questioning generally accepted medical analysis is met with a surprising amount of hostility.
Probably because it's so very very common and almost always utter bollocks.
People who would never think they were capable of comment on, say, nuclear reactor design with an hours study never the less think they're qualified to talk about the health effects of xyz based on about as much.
And sadly they get taken seriously, unlike in many other fields. news shows will include nuts who believe that vaccines cause autism for "balance" opposite the doctor but in the following segment on rocketry they don't feel the need to include someone who believe...
For example, what would be inappropriately off topic to post to LessWrong discussion about?
I couldn't find an answer in the FAQ. (Perhaps it'd be worth adding one.) The closest I could find was this:
However "rationality" can be interpreted broadly enough that rational discussion of anything would count, and my experience reading LW is compatible with this interpretation being applied by posters. Indeed my experience seems to suggest that practically everything is on topic; political discussion of certain sorts is frowned upon, but not due to being off topic. People often post about things far removed from the topics of interest. And some of these topics are very broad: it seems that a lot of material about self-improvement is acceptable, for instance.