>...the bone I pick is that there are so many people who believe it's just like the movie...
A movie, like an idea, is not responsible for the people who believe in it.
Where I object is when the makers of the movie (or book, or any other work of art) start making claims of historicity and then fail. Braveheart falls into that category, among its other failings. Dan Brown's Da Vinci Code was reprehensible but he continued to claim he'd done good research. By contrast, Umberto Eco took any number of liberties, but he generally stays true to both time and place in The Name of the Rose.
That last is a good example of another aspect of this. The details in that book were so specific, down to the conflict within the Franciscans at the time, that the author didn't need to claim any sort of historical accuracy. The book itself stakes the claim with its specificity. Many other books play fast and loose with the past and it's obvious they're doing it and we're invited along for the story ride, not a history tour. With movies one can look at Troy or the even sillier 300 as examples. If a viewer takes either at face value, well they get what they've invested. Hope they didn't pay too much for the popcorn.