I don't know about bad publicity though. To each customer support call simply say, Comcast has broken their contract with our CDN. Please call comcast. Considering Comcast is one of the two most hated companies in America right now, by a _huge_ margin, people will easily believe that, especially since in this case, it would be true. Level3 et all are enabling this behavior.
Nobody likes the cable companies. It would be very easy for someone to capitalize on that hatred to win public support for net neutrality; it's just a matter of crafting the right campaign.
The smaller ISPs are just following Comcast's example: "You mean we can charge multiple times for the same data without doing any extra work? Sign us up!" All last-mile ISPs will eventually realize they can hold everyone hostage, so long as there is no significant competition.
Small ISPs also like this because they typically are very heavy on paid, private internet and don't do much peering due to having small, localized networks. They stand to gain, proportionally, the most since they can charge the people the were previously paying for access.
