Actually, to be even more semantic, it is not and never has been illegal to breach a contract. You actually have a right to breach a contract, but once you have exercised the right you have to pay the price, and the price is something that will be determined by the judge. The law governs the consequence of breaking a contract, but doesn't make it against the law to break a contract.

Similarly, by bartering or selling coupons you're not breaking the law or acting illegally. In fact, the airlines would claim (wrongly) that you're not even breaching a contract, since they initially claimed that FF miles etc had no value. What you do do is violate the conditions of the program, and allow the airline to bring into play the punitive measures they mention on every cert.