The vision of consumers as utility-maximizers, and the downward sloping market demand curve--so that the quantity demanded of a product rises as its price falls--both seem so plausible.
But the former has been contradicted by a very well-structured experiment, while the latter cannot be derived mathematically without incorporating the distribution of income as a fundamental aspect of economics--and Neoclassical microeconomics ignores the distribution of income.
Friede Gard Lecture 03 The Market Demand Curve