I'm currently reading a book about the the age of Dueling. Coincidentally it that talks a lot about the consequences of negative political ads, especially in the early USA.
Basically negative ads
had to be anonymous because otherwise, under the social codes of the times, the writer would be challenged to a duel which he was honor bound to meet. His position in society actually depended upon it. If he ignored or refused he would be publicly pilloried as a dirty coward both verbally and in the press and likely shunned by the public as well.
One had to be careful not to insult a public figure like say Andrew Jackson for example because he'd not only literally kill you for it, he'd come off as just bravely and correctly defending his personal honor against a vicious (and now dead) low life slanderer. After all by the standards of those days a person who lets someone get away with insulting them without responding to a challenge is a dirty low life coward themselves worthy of similar scorn and exclusion.
BTW I recommend this book. It's been a darn interesting read.
http://www.amazon.com/Gentlemens-Blo.../dp/1582343667