"I'm always impressed by how much fighting evil feels like committing crime," Jayné says, in Darker Angels, as they make plans to kidnap a teenage girl to rescue her from being possessed/killed by the demon who is hunting her down.
This is one of the things I like about this series: in Unclean Spirits, taking out the supernatural bad guy goes down like a hit. In all three of the books, the main characters are stuck with the existing system of laws that say you don't get to be vigilantes; there's no exceptions made if your target is a shell of a human possessed by a demon. Nobody's like, Oh, it's okay, he was a vampire! It's not okay; even if it's morally right, it is still legally wrong, and the gang's got to stay under the radar.
In Unclean Spirits, we're told that Jayné's uncle was a demon hunter, and demons - "riders" - are bad shit. You might make pacts with some of them - the lesser of two evils; enemy of my enemy; etc. - but everybody agrees that all riders are bad for the humans they ride. Everybody who worked for Jayné's uncle, anyway; anybody who got their information from him.
But in Darker Angels, we meet some characters who aren't connected to good old Uncle Eric, and they make a pretty good case for certain types of riders being beneficial, not malicious. And if that's the case, then going vigilante on them isn't morally right, either, and now you're not Batman, you're just a bad guy. Framing the whole set of shenanigans as crime is very appropriate; it feels like committing crime because it is.
I like the way the moral clarity of demon-hunting is being pulled out from under Jayné's feet. She inherited superpowers and a vast fortune, but no instruction manual, and in Darker Angels that's really beginning to show. There's too much that Jayné doesn't know, and her ignorance has major consequences. Just having superpowers, and intending to be one of the good guys, doesn't actually make you the good guy. And having actually done evil is harder to recover from than merely failing to do enough good; I like seeing that play out.