When I did History at school we had lessons dedicated to nitpicking the historical inaccuracies so I'd wager people are trying to shed the image of it being a 'national film'
That aside, as a piece of entertainment it's very overrated and I find it despairing that it won the Best Picture Oscar. In the story, it suggests the reason for Wallace rebelling was a soldier slitting the throat of his bird. But later we see him getting it on with a French princess. And the way the English and Scottish characters interact is laughable, at times it's like pantomime on celluloid. On the other hand, I felt Gibson's performance was very good - I've lived here my whole life and still can't pull off a Scottish accent.