Is Saturn the darkest villain of One Piece?
In Chapter 1103 I feel Saturn is implying that he was sending out agents to abduct young women so he could rape them and make more guinea pigs for his experiments, since to him humans are only good to breed like insects.
Ginny just happened to be one of the unlucky ones, but you can clearly feel the perverted satisfaction in his voice when he realized he could abuse one of the slave children who escaped him from God Valley. He then gives his slaves a terminal illness and leaves them to die, but the scales turned in his favour with Ginny. He had the leverage to force himself on Kuma and Bonney to manipulate their bodies and keep experimenting.
Saturn is the direct opposite of Vegapunk, in a way Oda showed with them the two sides of science.
I think the Gorosei will just be pure evil, no flashback can redeem them. And this is only the first one.