Opt-in Censorship?

As I said to Ken Magill for his recent article regarding Truthout: From what I know of how spam blocking works, and how ISPs make the determination regarding what mail to block, I don't think Truthout's issues (being blocked at Hotmail and AOL) relate to their politics. I think they relate to their opt-in procedures, bounce handling, feedback loops, and whitelisting. The issues are technical, not political.