Professor Solum quite reasonably and correctly points out that the converse of my observation that law and economics scholars are Marxists is also true: that Marxists also believe in law and economics.
I think my comparison was funnier, and as muddled as I was that's all that was important. A true Marxist would say "So what? It's the same tools, but they're using the tools of economics improperly." That kind of response is usually a hint that the tools and results are completely irrelevant; that instead it is a matter of ideology, and occasionally of personal aggrandizement, not argument. I just find it funnier to find, say, Richard Epstein (far from the most radical law and economics scholar out there) sitting down with Karl over a few beers and finding out that they really don't disagree on as much as the Organized Right would expect them to disagree upon. The narcissism of the Left and of the Right often results in greater horror on the Right when it accepts a concept on the Left than vice versa.
What I was trying to get at was the invalidity of the "necessary and sufficient" explanation. Economic self-interest is a necessary consideration; it is seldom sufficient. If it was, why would the ultrarich end up spending so much money on art (often art of questionable value, but that's beside the point)? Whether that art is a van Gogh—usually available as an excellent lithographed copy for a few hundred dollars, not the millions paid for originals—or the "rich Corinthian leather" Ricardo Montalban extolled as a virtue of high-trim-line Chrysler products (which, by the way, is actually less durable than less "luxurious" seat coverings, including other leathers), there must be a rationale that is not solely explainable by allocation of scarce resources. If there isn't, I'm going to start painting portraits of myself missing an ear.