Eric Alterman, arriving late to the post-Journolist comment-fest, points out that, in many ways, it made liberals less ideologically cohesive:
Many of us could barely stand one another. People argued over everything, not always civilly. Not long ago, I received an e-mail from another member reading: "I'm starting to understand what conservatives don't like about liberals!" I took issue only with the word "starting."
I had the same reaction numerous times, some of them referring to Alterman himself. I think this was especially true for the more moderate liberals. For people like me, the national debate mostly revolves around a liberal-moderate-conservative axis, and more hard-left or even traditional liberal views are fairly marginal. Journolist brought people like me into contact with a lot of those sort of liberals, and my main response was to realize that I'm a lot less liberal than I had thought.