A long time ago, Charlie Stross wrote a Rant against dejanews. It's here.
His thesis is this: universally accessible archives of usenet writing is morally equivalent to universal surveillance, and destroys not just privacy but also deniability -- Anyone can go back through the archives and find out everything you've ever said.
Which has been true for as long as I've been on the 'net.
Interestingly enough, this hasn't stifled discourse at all; instead, it's presented some evolutionary pressures: pseudonymity is now much more widely accepted, and deniability is built into most of what we write online. Usenet is less populated now that it was, and even its successor -- the web forum -- is hearing the baying of the hounds. Additionally, the very culture of the 'net operates to extinguish debate, which creates structural/cultural barriers to participation that make everyone think twice about the validity of what they're about to post.