There is a second avenue by which bankruptcy, and so, the leverage of firms, might impact the economy. Expected bankruptcy could result in an increase in the demand to hold money. If the quantity of money remains unchanged, or increases by less than the demand, then the result would be a shortage of money and lower nominal expenditure. If prices, including the prices of resources like labor, are less than perfectly flexible, the result will be a decrease in real expenditure, real output, and employment throughout the economy. The associated losses could result in widespread bankruptcies.
It is obvious that those who have lent to a firm would like to avoid losing money from default and bankruptcy. If they expect bankruptcy of some particular firm, they are motivated to sell the bonds of that firm. If they purchase bonds from some other firm, then there is no effect on nominal expenditure. In fact, they could use the proceeds of bond sales to purchase just about anything, and there is no impact on nominal expenditure. They might purchase stock, equity claims, presumably on other firms. They might purchase capital goods, starting a new business. They might go out to eat, using the proceeds of their bond sales for consumption.
The problem only develops if those selling bonds due to fear of default simply hold onto the proceeds and spend them on nothing. Many people, including economists who should know better, assert that as long as the accumulated money is kept in a bank rather than under a mattress, this won't cause a problem. However, the most likely scenario is that whoever ends up buying the bonds already had the money in the bank, and so the transaction simply shifts balances in checkable deposits from the seller to the buyer. Unless the total amount of money created by the banking system expands, then there is a shortage of money that needs to be corrected by a decrease in all prices, so that the real quantity of money rises to meet the demand.
Superficially, if firms are highly-leveraged, then they are more likely to default and become bankrupt. Fear of bankruptcy could lead to an increase in the demand for money. An increase in the demand for money, if the quantity of money is unchanged, leads to a decrease in nominal expenditure. The decrease in nominal expenditure leads to recession. Therefore, increased leverage leads to recession.
However, there are problems with the argument. Suppose firms had no leverage and were financed entirely with equity. If stockholders expect a firm to lose money, they are motivated to sell their stock. They could use the proceeds of those sales to purchase any number of things, including shares in other firms that are not expected to lose money. However, if they choose to hold more money, and the quantity of money doesn't increase, then the result is lower nominal expenditure.
Obviously, the key problem isn't the makeup of the finance of the firms--debt or equity--it is rather than the firms are expected to suffer losses, and when investors try to avoid those losses they might choose to hold more money. Is there any reason why additional leverage might be expected to exacerbate this problem? If debt is a closer substitute for money than equity, then an increase in the expected loss from debt might cause a larger shift into money than an equivalent expected loss on equity. Variation is expected profits for firms with higher leverage might result in a higher variation in the demand for money than the same variation in expected profits for firms with lower leverage. The more similar the debt instruments used to finance firms are to money, the more serious this problem.
However, to conclude that fluctuations in nominal expenditure are caused by over-leverage depends on assumptions about monetary institutions. If the quantity of money changes to accommodate the demand to hold money, then even if an increase in expected losses increases the demand to hold money, nominal expenditure would be maintained.
The monetary disequilibrium approach should never be confused with old-fashioned monetarism. There is no assumption that the demand to hold money (or equivalently, the velocity of money) is unchanging. There is no hidden agenda to argue that there is some aggregate of monetary assets whose quantity can and should be kept on a stable growth path. The monetary disequilibrium approach focuses on two things. First, that changes in nominal expenditure are due to an imbalance between the quantity of money and the demand to hold money. And further, that prices and wages are not perfectly flexible so that the market process by which changes in prices and wages cause the real quantity of money to adjust to the demand to hold money results in undesirable fluctuations in output and employment.