I can understand why enemies of free markets use the term "market failure" because it presumes that "regulation success" will shortly follow. I don't understand why an economist would use that term, however. Markets don't "fail". Markets sometimes generate results we neither understand nor like. It is an act of hubris, however, to call that a "failure". Do we call an "earthquake" a "geology failure"? Do we call a hurricane a "weather failure"? Of course not -- the idea is ridiculous.