I actually think delving into the darker side of yourself to pull out nasty characters is therapeutic. It's better than letting some things fester, and it helps get some of the author's darker emotions and feelings out where they can be safely expressed. Sure, you're going to a bad place in yourself, but it's better to acknowledge that bad place is there and deal with it, I think. To put the genie back in the bottle, I think honestly just knowing why it's there would help. A little introspection never hurts, and could add a lot of depth to your writing. The better you know yourself, the better you know your characters.