Imagine: you are working at a cash register and a someone brings his purchase up. When he then attempts to pay using a 20$ bill stapled to a 10 foot wide poster board with child 9orn printed on it. He then proceeds to complain that you are censoring his transaction because you will not accept his form of payment. He argues that he paid full price for the posterboard and printing and that the free market should decide what transactions are valid. You reply: sir, the free market just did decide. Run knots.