My son just put the question to me (I was commenting on Facebook at the time), and I thought some here might be interested in my answers:1. As an excuse not to work on my current book. The chapter drafts I have just been looking at are in worse shape than I thought, which is depressing.2. In the hope that by putting ideas out, some of them will spread, with some (small) effect on the world. Posts here probably get more readers, but comments on Facebook reach a different audience, one less likely to be familiar with the ideas.3. In the hope of finding someone reasonable to argue with, which might result in changing his views, or mine, or both, in a desirable direction, as well as being fun. It happens very rarely, perhaps once every few months, but I'm an optimist.4. Because arguing with unreasonable people online, and watching unreasonable people argue with each other, gives me useful, if depressing, information about what such people are like and (I hope an exaggerated) picture of how common they are. Like most people, I live mostly in a bubble, interacting with a very nonrandom set of people, and this gets me a view outside it. The same is true of reading trade chat in WoW, also depressing.5. For the same ignoble reason that people spend time beating up on NPC's in WoW and similar games.
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