My basic understanding of it is that it encourages malinvestment which leads to bubbles and the market cycle of booms and depressions.
Further, I think that the fed keeping interest rates low causes inflation and the devaluation of the currency because it's only possible to keep interest rates that low by printing more money, but I'm not sure about that one.
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_foolmo_
'Illegal activities is a slight misnomer, most of it is not related to material that is actually illegal.' - nintendogrl1