Even by Sith standards, Palpatine truly stands out as being a complete monster. I mean, he didn't have the greatest childhood, and I thought it was reasonable he killed his father, but he then goes on to callously kill his whole pathetic family to satisfy his rage. His master discontinued the Rule of Two, and genuinely grew attached to Palpatine, but in turn, Palpatine tortured him viciously, and killed him in a pathetically cowardly fashion, which in turn, is against the Sith code of strength. He betrays all of his apprentices, quite literally, and instead of being satisfied with his absolute control of the galaxy, he feels the need to commit genocide, for no reason other than for fun, as Vader once stated. But in the end, why is he so evil? I mean, Sith are evil, but there are Sith that are just neutral-evil, or past Sith that didn't stretch out like Palpatine. He's just a completely irredeemable monster.