They created literal slavemaster beings. Agates. Literally programmed to be the most awful thing imaginable. They created literal monsters. They had a program template designed specifically to be horrible.
"An Agate Terrifies"
And now that the Gem Wars are over, they have no place in the universe. Being literally created with an obsolete and horrible purpose.
I think that was a major missed opportunity to explore someone like an Agate learning how to heal from something like that. If that's even possible. The philosophical implications would be really cool.
spoiler
She was one of the nobles. Instead of confronting them, she faked her death and declared war to free Earth.
She had a lot of patronizing views on humans and instead of confronting her family outright, she might've caused less damage. Then Steven more or less worked to redeem pink's family of colonialists.