Wasteland 2 - you can be pretty evil and even go all out rogue, like turn against the Rangers and take over Arizona with some enemy faction.
Age of Decadence - kinda encouraged to backstab and never show mercy to your enemies, particularly if you're playing an assassin. To a ridiculous extent, really. It's like everyone's out to use you and everyone lies to you, so you end up doing the same.
Carmageddon - you play a deranged racer in a death race where you murder pedestrians and other drivers.
Dishonored - you've always got a choice between disabling your target and killing them. But a lot of the "disabling" options seem worse than straight up killing. Like you can condemn some people to having their tongues cut out and a life time of slave work in the mines, and you can help a creepy stalker kidnap one of your targets.
Fallout New Vegas - lots of chances to be a bad guy, and you can side with the really morally questionable people in the main story.
The Guild 1 and 2 - you control a family of manipulative entrepreneurs with the ultimate goal of eliminating all other such families. You do this through gaining and exploiting seats of power. You can engage in gold-digging, bribery, nepotism (including being a judge in a family member's court case), falsifying evidence, poison, kidnapping, mugging, piracy and straight up murder.
The Hitman series - you're an assassin with really questionable moral values. For the most part you go after scumbags, but some of the targets aren't as deserving. And the usual chance to murder guards, police and civilians applies.
Hotline Miami - you're a most likely drugged up far right nationalist murderer. At one point you even murder everyone at a police station just to get at a target they arrested.
EDIT: I sorta misread the OP and just went by the other suggestions, so the suggestions are not quite what was asked, I realize. So I've unbolded the ones where you're just evil fighting neutral-evil. And only Hitman and Hotline Miami have it as something non-optional (in both you end up fighting police forces just doing their job).