I HAVE put negative stuff into scenarios before (I must have been either too perverted or too insensitive to my clients’ morality). I did so only because it reflected some of what I observed in people.
User scenarios are at best hazy predictions, and at worst, a wishful, rosy projection. That said, I am not convinced that if something seems “negative,” that it is necessarily a better insight. It is just a different insight.
Some negative assumptions about human nature, coupled with technology are examined in the interesting work of Dunne and Raby
http://www.dunneandraby.co.uk/
I suppose that a more expansive view of user scenarios can be found in William Gibson’s fiction - i.e. when he sums up his approach with something like this: “I take plausible technologies of the near future, and then imagine them in the hands of common criminals.”