While I do not disagree with you altogether, I have a hard time believing it would be possible to come up with some sort system that is inclusive of these exter

While I do not disagree with you altogether, I have a hard time believing it would be possible to come up with some sort system that is inclusive of these externalities. Look at what a crapshow nutrition science is - do we really want government encouraging/discouraging foods more so than it already is? Look at how bad farm subsidies have affected our health in general.