Andrew Sullivan, in the new Atlantic, explains why he blogs:
Each week, after a few hundred posts, I also write an actual newspaper column. It invariably turns out to be more considered, balanced, and evenhanded than the blog. But the blog will always inform and enrich the column, and often serve as a kind of free-form, free-associative research. And an essay like this will spawn discussion best handled on a blog. The conversation, in other words, is the point, and the different idioms used by the conversationalists all contribute something of value to it. And so, if the defenders of the old media once viscerally regarded blogging as some kind of threat, they are starting to see it more as a portal, and a spur.
For references to Plato, Pascal, Karl Kraus, and Montaigne, read on.