It is known all the assumptions understood in the economists conception of "rational" behaviour for a consumer, the consumer's demand curve can be resulting from an infinite knowledge of the consumer's budget and partialities. The interpretation of this extremely theoretical (hypothetical) relationship between price and quantity ordered of a certain good is that, given all the other goods and controls, this set of choices is that one which makes the customer happiest.
A key tread in microeconomic theory is the one which extends the aggregate or market demand from the large collection of human being demands. A significant question is to understand the interpretation of the market demand curve. Does the aggregated demand curve show how to optimize the total utility (happiness) of society? Does it show how to optimize something else?
It cannot optimize total value of society, since:
1) Each person's individual total value gleaned from purchases depends on the size of her financial plan, but the distribution of wealth (and thus her budget) is a part (free) variable in the aggregation. In other words, changing the allocation of wealth (such as giving needy people more resources) will create a different total for society's utility.
2) Each person's demand curve is a purpose of her budget, so that if the allotment of wealth changes (by changing the distribution of costs and thus salaries, and so on), all of the individual demand curves change. The collective effect of such a change is not simple unless all the customers have wealth-independent consumption patterns that is, if not the pauper and the billionaire spend very similar fraction of their budgets on each item.
Given that the sharing of wealth is a function of cost levels and is in general a free variable in any attempt at social optimization, markets cannot be maintained to select by themselves neither equilibrium nor an optimum.
Microeconomics ignores the issue of wealth distribution, assuming it to be a separable "political" issue; however, in the context of conceiving of a market demand curve, as in many others (e.g., worldwide trade), microeconomists implicitly take for granted that wealth giving out is flat i.e., that wealth levels among components of society or dealing partners are equal.
It is remarkable to note that one method of explanatory the aggregation of individual demand curves is to divide society up into a variety of economic "classes" and to build the assumption that each class has a coherent set of partialities and a relatively inflexible level of wealth. Then different demand curves could be developed not for every part of market, but for different classes. Such an inflexible system is clearly not a "free market", in which prices affect wealth through employment, and economic mobility is in theory unlimited.