@Ivy i appreciate that. i will try to keep it civil as well.
first, marxist try to root their LTV in classical economics. especially Ricardo. Adam Smith was more clear that this was not how he saw things, i think his elaborations make him a sort of proto-marginalist.
the fundamental problem is: if value is the same for both parties, then they have no reason to trade.
i think economical purpose of LTV is to "explain" prices.