In my experience when someone has good information and sound logic behind their position they welcome opponents, because its through debate that they can really show how much better their ideas are. However when someone fails at making logical arguments for their case they will often tell their opponents to leave, or shut up, and try to disparage their credibility, typically by attaching a negative label to them; this typically makes the problem worse because the party doing the labeling recognizes the inherent flaws in this method and this generates insecurities. The better opponent (who is often equipped with an inherently stronger position) who is winning is thus the source not only of a threat but also makes the weak opponent uncomfortable with themselves. Something to think about when you are trying to get someone to not object to what you are saying.

So, most of the time it's alt med advocates who bring up the subject of mainstream medicine.

There are instances where a poster asks about an herbal treatment for a problem, and is advised to seek an accurate diagnosis first from a physician before pursuing any treatment. This is not meant to rule out herbs or supplements as eventual treatment, but some find it unacceptable and threatening to mention physicians in any context other than a critical one.

As for ad hominem/personal attacks, the best strategy is to disregard them and only address health-related remarks and questions. Once trolls realize they can't get a rise out of opponents or spark a flame war, they usually get bored and leave.