Yggulf the Mute has dialog for the "bad people" topic used in http://en.uesp.net/wiki/Morrowind:Larrius_Varro_Tells_a_Little_Story
Suggested fix: add an entry just for him with his usual mute response.

Looking at the dialog editor, there are several more topics that might need this fix, though they seem less likely to occur:
anonymous writer
Big Helende
Gentleman Jim Stacey