Count me in the "can't play evil well, too fluffy inside, will cave eventually" club. But I AM a Paragade deeper in my bones than anything else, and that's my window here--in my opinion, someone who staunchly upholds the law even in a case like that of a killer from Dragon Age 2 is actually less good than someone willing to kill him. The situation, for anyone who doesn't know, is that you are hired to bring in a serial killer... and when you meet this serial killer, he literally BEGS you to kill him in a moment of clarity after almost harming a sweet elven girl. She begged you not to, and you're only going to get paid if you complete the contract as ordered, but the killer himself knows two things that he uses to persuade you: 1. his father, the magistrate, WILL let him go again and no one will override that decision. 2. He WILL kill again; he isn't sane enough and doesn't have the willpower to stop. This being let go and killing again is a pattern that has already repeated.
I think in a case like that, it's pretty clear that the good and selfless option is to actually just kill him (assuming you are wise enough to believe him, in this case). Letting him go to spare your own conscience and get paid a few coins also causes a lot of deaths of young elves. For context, in this universe there are no asylums, and people who are different are largely treated with ignorance and fear--plus his father would just jettison him anyway even if you could put him in an asylum. Knowing this, the lawful choice is also evil. No good you are doing by letting him live outweighs the stream of innocent dead that follows.
So in other words, I'm saying... if you take that just a little bit further, I think you can make a more vicious well-intentioned person who thinks you need to do tough love to scare the weak, while those who are strong but excessively cruel should die. Even the worst evil person might regard their own safety as a factor, especially if a vampire, and thus want to take out the strong leaving only a herd of weak civilians around them. Imagine being an evil bastard who gets the adoration of every town she passes through, with very few people actually knowing the truth. So you could do good for bad reasons, or bad for good reasons.
I can't really persuade myself to be cartoonish or insane evil, that's not fun for me... but I'll definitely be a more ruthless sort, brutal and unafraid to dirty her hands. One can be pragmatic and good at the same time, I think, especially if more chaotic in nature. I think the worst I can do is Dexter--evil that serves a positive purpose. Sadism that is only practiced on those who really earned a taste of their own medicine.
