Eliezer's point in that post was that there are more and less natural ways to "carve reality at the joints." That however much we might say that a definition is just a matter of preference, there are useful definitions and less useful ones. The conceptual analysis lukeprog is talking about does call for the rationalist taboo, in my opinion, but simply arguing about which definition is more useful as Eliezer does (if we limit conceptual analysis to that) does not.