But it wasn't Dumbledore, Snape, or anyone else we've seen messing with memory technology who didn't believe Harry. And if Fudge was so certain he was right despite all the evidence before him, a conjured up memory wasn't going to help.
As to the film, I have some very bizarrely mixed feelings. Overall, I enjoyed it quite a bit. But given that the 6th book is my favourite by a mile, this film fell short of the standard set by the 5th, imho. The main issue, as others have stated, was that the story of the book seemed to be laid aside to facilitate too much focus on the teen-romance parts. Not that I dislike these parts of the story, and in fact I think they did the scenes well in the film, particularly the bit where Harry comforts Hermione on the stairs. It's just that, if time is that limited and you have to cut so much, why cut the whole point of the book - the Voldemort backstory flashbacks? We only get one memory other than the important Slughorn one, and as such it plays too much like a token Superhero origin flashback, where we see a single defining event and then fill in the blanks in our head. Adult Voldemort's absence is barely noticeable in the book because younger Tom Riddle is so ever-present. But in the film, we see so little of him in any guise that he is conspicuous by his absence.
In short, the film suffered more acutely than the previous ones from a disease they nonetheless shared - a fairly bizarre sense of what to keep and what to leave out from the source text. Was that whole sequence on the train really that vital? With that time, we could have had another entire Riddle flashback.
I just found myself shaking my head afterwards at the creative choices that had been made with regard to pick and chosing material from the book.
Having said all that, what they did choose to do, they did very well indeed. The cast have matured into a coherent, interesting group of actors with some real talent in many quarters. Malfoy has improved leaps and bounds from his early days, but again Snape stole the show when it came to the 'bad guys'. The core three actors have wonderful chemistry together, and I was particularly impressed with Emma Watson's improvement over the previous films. Always, imho, the strongest actor of the three, Rupert Grint puts in a very solid performance indeed, and carries off all the humour effortlessly.
The 'support cast' of the film series barely make an appearance, Bonnie Wright's increasingly faultless Ginny aside, and while this is a shame, it did bring a much better sense of isolation for the core characters which is in some ways an improvement over the book. Often in the written story, it was hard to imagine the 'us against the world' feeling pre book 7 because we simply knew so many Order types and so few Death Eaters that Voldemort couldn't help but feel outnumbered. In the film, however, the destruction of the Burrow and Hagrid's hut, along with the very short screen time or total absence of many Order members (Mad Eye Moody, for example, doesn't even get an appearance), lead to a real sense of the characters' world collapsing around them.
Overall, I'd rate it above average. What is in the film is excellent-rated stuff, but there are too many sins of omission for me to grant the film an overall excellent.