Yep,"discussion" forums are best looked at as entertainment - bar talk, not consultancy. There may be opinions you agree or disagree with, but you shouldn't do anything except take the ones you find interesting on board, but ultimately rely on your own judgement and direct sources of information.
People tend to mix up fact and option on forums, and people often confidently state things that are simply untrue on forums. There's no accountability on a forum.
A forum post should never be a person's sole basis for making a purchasing decision.
That said, the MR forum is huge, and I'd make a distinction between "opinion "topics / threads and technical threads. Where forums are still very useful is when you are looking for a solution to a very specific technical problem, whether hardware or software. Those type of forums, discussions and threads are very different, and there isn't the same amount of foodfighting - the fix either works or it doesn't.