More national defense means less of something else that society may value more, like health care or Social Security. To be efficient, additional goods from the public sector must also follow the rule of rational choice—pursue additional government activities if and only if the expected marginal benefits exceed the expected marginal costs. It all comes back to the adage "there are no free lunches." Governments provide an alternative method to markets for supplying goods and services when it appears that the benefits to society of doing so outweigh the costs to society. Not all individuals will bear the same costs or share the same benefits of those policies. A government policy to correct a market imperfection is not justified economically if the cost of implementing it exceeds its expected benefits.