Valid legal contract = offer + acceptance + consideration. There's no requirement that consideration be adequate, only that it exist. Multinational corporations sign millions of contracts with each other every day for the princely sum of $1.
In certain cases, mistake being one of them, the general rules in contract hold that valid contracts may be rendered void or voidable, subject to any over-riding legislation. The DOT rules have over-ridden this general principle: with respect to airline tickets, mistake is no longer a reliable defense to unilaterally repudiating a contract.
Ethics, morality, and intentions are all fine discussions, but they are irrelevant to the question of whether the law requires these tickets to be honoured. So are all the analogies to other types of purchases.