Over a beautiful sunset, the machines send their Colonel Sanders avatar to announce that any humans who want to be freed from the matrix will be allowed to do so. Thanks, Neo!
Wait a Minute...
Hey, remember in the first movie where they said they don't pull adults out of the matrix? You know, because finding out that every experience they ever had was false and that the real world is a frozen wasteland destroys their mind?
Well, in this new world, the whole, "All of society, history and culture is a computer generated hoax" thing isn't going to stay a secret for long. How do you think society would react to finding that out? How do you think the major religions would react?
Why would anyone get up to go to work after that ("Build a house? Why can't the matrix just freaking generate one")? How do you think starving third-world nations would regard their machine masters, knowing that their misery is purely the invention of the machines, and that the matrix could in fact have rained food down from the sky any time it wanted, but just chose not to?
The world would descend into utter chaos. Luckily, the people can escape the madness any time they want by exiting the matrix!
Oh, wait, they can't. The one city where people can live has been devastated by the robot attack, and there is nothing close to enough housing, food, clothing, fresh water, etc to accommodate even a small country.
Fuck you, Neo!
The "Happy" Ending:
While on a time-travel adventure, young Marty McFly helps his father become less of a pussy and meet his future wife. After returning to his own time, Marty finds that his formerly dysfunctional family is now happy and affluent, the school bully Biff has been made into an indentured servant, and he has a cool new truck.
Wait a Minute...
Marty's family doesn't exist anymore.
Sure the people in his house look the same, but they have completely different personalities from the people he knew and loved before he hopped in the Delorean. The utterly different direction their lives took basically gives his parents personalities as alien to him as pod people from Invasion of the Body Snatchers.
Not to mention the fact that every single conversation and interaction with his parents will be based on a history he has utterly no memory of. How long until they push to have Marty institutionalized, since every memory from his childhood is from some bizarre alternate reality that no one else shares?
On top of all that, while the movie wants us to cheer Biff becoming a menial laborer for the McFlys as a nice bit of karmic comeuppance, we can't help but think that it's a bad idea to give a house key to the guy who once tried to rape your wife.
But hey, at least he got a cool ass truck out of the deal.
For movies that are depressing for a whole other reason check out Rick's look at 5 Awesome Movies Ruined By Last-Minute Changes. Or find out about some action stars whose careers had a less than happy ending in 5 Movie Martial Artists That Lost a Deathmatch to Dignity.