When Diem refused to fight corruption in his own government, reform his armies, and win the loyalty of the hamlets and villages in the Vietminh dominated areas of the countryside, the U.S. should have walked away, with the realization that victory was not only unlikely, but impossible. The key difference between Viet Nam and Rwanda and Bosnia and Sierra Leone is that the latter three nations are not proxies for a world superpower conflict. They do not require the U.S. to make an alliance with unsavory dictators, and pour in military aid to prevent some expansionist foe from gaining the upper hand. And Russia is not only not interested in manipulating the crisis, but incapable of financing proxies. Cuba is out of the picture.
China cares only about internal security.
The U.S. is free to intervene on behalf of freedom, peace, and justice for all. They are free to be the good guys. How ironic that they no longer want to play. The inherent absurdity of bombing Serbia into submission is that bombing does not threaten the interests of the ruling class. The war footing ensures the success and acceptance of martial law.