Janus Marius
Plo Koon Rulez!
Hm. Good question.
1. He killed Master Syfo Dias.
2. He attempted to bring the galaxy into a war which would kill millions, possibly billions as a means to an end.
3. He paid two bounty hunters to kill Senator Amidala.
4. He attempted to execute her again, along with two Jedi.
5. He was a royal dick to Ventress and just about anyone else who worked under him. He was also supposively a racist, but I still think that addition was kinda lame and unprecedented in his behavior.
6. He believes cloning is okay. Well, okay, that's not a bad thing, but he basically paid for millions of clones to be grown so they could be blown apart by robots which he was also paying for. That's just the supersized version of a rich kid playing with toy soldiers.
7. He probably did some bad stuff in the comics and the cartoon series, and a bunch of other spin-off bullshit that I didn't read because I don't have tons of money.
So he's pretty morally bankrupt. Perhaps higher than I thought before putting this together, but he's hardly a Sith when you think about his real reasons for doing any of this.