[lrm242]

First, I never claimed the markets were or were not zero-sum, only that your attempt to explain was wrong as it mixed realized and unrealized profit.

Second, zero sum requires a definition of utility for each participant. If those definitions vary (and they almost assuredly do) then a reasonable argument can be made that to define whether the activity is a zero-sum game or not requires a commonality amongst those utilities (dollars, for example). This is often not the case in trading (for example, the farmer hedging his crop with a speculator who seems to profit short term).