Edit: Doing a search for the title shows that it's been the main tradition for ~ 2 years. So that line of reasoning seems a little suspect.
But it's worth emphasizing Scott doesn't participate in that thread, and he doesn't necessarily like it either. In fact, from what I can tell he's not a huge fan of lots of the conversations that go on there, and the topics discussed.
If anyone were to judge him on comments, please only do it based on the curated comments on his website, where he deletes and bans people who are uncivil.
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As I'm sure everyone has noticed, the culture war thread has essentially grown to devour all of /r/SlateStarCodex. Also, we talk about really weird stuff here. That's intended, and it's something I like about this community; however, given the weirdness, Scott Alexander no longer wants it on /r/SlateStarCodex. We're moving this thread to another subreddit, and after some internal discussion, we've realized that only a subset of our moderators want to be responsible for the new culture-war-specific subreddit. ----
So it's definitely not Scott's discussion.But politics exists, much real stuff happens there, and also, it's great entertainment. It's also great training, if you don't succumb to bad thinking. It's better doing in company of people who try to be civil and use logic, even if it usually barely works.
Resolving this tension is part of Scott's writing from very early on. This is not just image clean-up, it's dealing with a difficult situation.
Not so much that, but to avoid repercussions in his real life. There are topics being discussed that are real sacred cows, and even if his conclusions are "correct", sometimes one is considered evil just for daring to question the conventional values. (indeed, that's much of what the "culture war" thread is about)
Since his writing is just a hobby, he doesn't want fallout from that to impact his real professional career.