First of all the wording I provided in my earlier post is an example of what the airlines could place in the COC if too many people start refunding tickets for security refusals. not an actual cut and paste from UA's COC.

Second, I think that if enough people started refunding the tickets under the rule 260. The airlines would change the terms that you agree to when purchasing the ticket to make it clear that screening is done, and that refusal will not be grounds for a refund. Contractually they can hold you to those terms because they fully disclosed the screening (that it will happen) to you, told you the procedures were out of their hands, and it is a term of the sale. Further because screening is done by the government, then any action done at the checkpoint would fall under the restraint of princes clause in the COC, which essentially states the airline is not responsible for government actions, and no refunds will be given because of government action. it is a risk of carriage.

In the end whether we agree with the procedures or not, if too many people take advantage of this clause, it would soon disapear. Further those who "abuse" the clause could easily find themselves unable to book tickets or fly the airline they use the clause on. In essence they would be banned from the airline because they are too much of a pain and a drain on the airline's finances. In most cases it would probably occur after the second refusual. The first one, the airline could say, you didn't know what the screening meant. After the second one, you couldn't say that, even though the rules change faster than anyone can follow.