I enjoy good characters, people with at least a little complexity.

Building tension is good, so is consequences. Tension and consequence are probably the foundation of a good blackmail story.

I don't have a problem with needing the victim to deserve their punishment. I very much enjoyed reading Allie and Nicole and much of that enjoyment was probably derived by the fact poor little Allie didn't deserve her fate. Group XS was another great story filled with poor unfortunates suffering for no karmic reason.

I have read some stories that sickened me when I realised I enjoyed them. Stuff by Llabmik certainly springs immediatly to mind, but there are plenty of authors around here who are responsible for perverting me. And I thank them.

I remember one of the first stories I wrote for my own enjoyment I eventually deleted when it evolved to a point where what I had created disturbed me. These days I just accept that if I write something it's coming from within anyway and there is no point in censoring it.