I don't think there are many people on the internet who haven't written anything "stupid" at one point or another. Especially when involved in commenting on a social news site.

I wonder what percentage of Digg/Reddit/Slashdot/HN readers have made at least one comment that could justify investigation? Keeping in mind that even a vague statement like "I wish someone would kill (x)" has been considered justification for some police departments to investigate the author. Probably a nice big percentage.