Risks of Partisan Spam Filtering?

Mike1024 asks: "Pete Klammer reported in RISKS 23.95 about spam filtering software filtering political e-mails - including Postini blocking certain anti-Schwarzenegger URLs and Comcast blocking e-mails mentioning afterdowningstreet.org. This could be caused by malicious action, misreporting of spam, 'joe jobs', or actual spamming. With many people using their ISP's default settings, and manual spam filtering being impractical for many users, what can be done to avoid giving ISPs and anti-spam companies extensive, fully automated censorship abilities?"