@SteveRoth our models of U(c) for general consumption look nothing like this. they are always nondecreasing. we can never, in the model, be made worse off with more consumption. economists justify this shape by letting c refer to a vector of the potentially infinite goods we might buy, and by presuming "free disposal" (if the extra ice cream would be bad, we can throw it away, so in fact an extra cone can never hurt us even if it doesn't help us). 6/