movies with 'happy endings' that are really fucked up when you think on them

about as happy as you can expect from a Michael O'Donoghue script

Dune (1984)

from Wikipedia: Paul demonstrates his newfound powers and fulfills the Fremen prophecy by causing rain to fall on Arrakis.

however there's a tiny problem with that: it kills the sandworms, ending spice production because the sandworms are integral to that, ends practical interstellar travel, and effectively causes the collapse of human civilisation

re ET, AI, Dune, I wonder who would win in a three-way shootout of movies with ostensibly happy but fucked up endings between Spielberg, Kubrick, and Lynch?

Nicole Kidman telling Tom Cruise, "Git yer boots on cowboy, it's humpy pumpy time!" feels like a top contender...

the parents in Time Bandits sucked, so them getting vaporized and Kevin being free to do whatever he feels like IS a happy ending, we loved it as kids