This is true about so many things. Sometimes people are driven by their knowledgeable and passion, but there is also a large group driven by selfish desire to promote themselves or an agenda. The guy who wants to be in charge so he can be in charge instead of lead, is not the guy you want in charge.
It's amazing how much wasted energy is spent on pseudo science. From zero-energy devices to "secret" cancer cures. Those involved create boogie men(usually the government) who are repressing "the truth", as the actual data to support their claims is weak. Rallying people against a common enemy is easier than coming up with an actual product that works. It's incredibly lazy, and usually a few minutes of research will cast doubt on claims. The scamsters are scum, but you can see the motivation. Those who actually believe are scarier.
I don't think you really get medical advice from CrowdMed.You get ideas for diagnosis(probably with reasoning) - and you go with them to your doctor, to verify.In general CrowdMed deals with cases where regular doctors failed to find a good diagnosis,so they will be happy to get GOOD ideas.
I'm skeptical that's true in medicine, though it depends on how else they filter their community. My own experience is that non-doctors with strong opinions about medicine that they feel motivated to share are usually precisely the people you don't want medical advice from. Often they are adherents of one or another alternative-medicine system, or otherwise have really idiosyncratic views.