The only reason to buy an instrument is that it is cheaper than the cash cost of flying J. The only reason UA issues instruments is to build loyalty, e.g. future spend to make up for the diffeence.
It seems fairly simple logic to have a rule prohibiting the sale or barter of the instruments and to penalize their misuse accordingly. It does not make sense to fire the customer altogether as many have little or no choice and will still continue to fly as before.