In the late 1970s, there was a major controversy over a dam built by the Tennessee Valley Authority called the Tellico Dam, which is located near the mouth of the Little Tennessee River. After construction was completed and almost all of the land purchases (or evictions) had been done, the Supreme Court ruled that it could not go on because of the presence in the Little Tennessee of a fish on the endangered species list called the Snail Darter. (Congress later voted to exempt the dam from the law and the dam was closed in the late fall of 1979, creating Tellico Lake.)

While the economic benefits of the dam were admittedly dubious, one of the common arguments for completing the project was this: "We have spent more than $100 million to build this dam. We need to complete it because we will have wasted all this money otherwise." Please evaluate this argument from an economic point of view.

Please explain in details.