I don't think this is necessarily fair. People expect guard dogs to provide protection from unknown intruders. I wont ask why you were entering peoples homes when they weren't there but if this was for a legitimate reason they either should have been there to control their dog or had their dog housed elsewhere while you had to visit.

Statistics will always trump empiricals. The one unfortunate problem is that where pitbulls have been banned, they often get renamed or mixed with other dogs to allow people to continue to have access to extremely violent dogs e.g.: