If there are about 1,800 freshmen at Harvard each year, then Harvard could admit, say, 100 competitive applicants whose fathers (typically, hedge fund guys) write the Harvard Number on a check -- without tangibly lowering the quality of the class. That's, theoretically, a half billion per year in virtually free money. How could an institution resist that temptation?
Quid pro quo arrangements aren't supposed to be tax deductible as charity, but how often does the IRS get the goods on this? In practice, a big chunk of the Harvard Number gets refunded by the taxpayers.