I understand the dangers, but they of viewers' naivete, laziness and/or stupidity not of the movie. It's like believing every post you see on the internet. Yes, if the movie's producers sell it as fact, they have a responsibility to be true to their word, but it seems to be always "based on actual events". It's up to us to suss out the truth.
I used to get upset about factual errors too, but I think I can trace my change of heart to the movie "JFK". It was filled with errors of fact and intent, (and the passage of time has proved it to be even more inaccurate), yet it remains one of my favorite movies of all time and I highly recommend it.
On the other hand, the movie "United 95" purports to be factual and lives up to that as far as it can. But even there it depicts moments on the plane that no one could know happened, but these moments fit in with the facts that we do have and the viewer believe them, not believe them or just watch and react. Directors are artists not historians.