The gross annual production of petrochemical plants situated in the Jamnagar district of the Indian state of Gujarat is around 130 million tons. Each plant follows the profit-maximization principle and supplies petrochemicals up to the point where price equals the private marginal cost of production. Industry experts claim that the aggregate production of this industry is socially efficient because at this output level the supply of petrochemicals is equal to its demand. Which of the following, if true, would strengthen the claim of the industry experts that production is socially efficient?