I sometimes think there's more discussion, hand-wringing, and angst over HCT on FT than there is in the UA (and DL, AA) boardroom. Here's how I view the topic from 30,000 feet (31,000 if Eastbound):

1) The major carriers want there to be gross pricing imbalances as it allows them to make much more money in important (to them) markets.
2) The major carriers obviously know the incentive for HCT can arrise from these pricing situations which they create and generally benefit ftom.
3) HCT is a minor enough issue to them that even though they might not like it, they put up with it as a not much more than just an annoyance in the big picture of advantageous pricing.
4) The major carriers prefer to not let HCT get out of hand by going after habitual "offenders" and, for the most part, don't worry about the rest. They must not think they have much legal standing to fully shut it down as they never go down that path.
5) The major carriers still end up making far more money than they would if they were to revise pricing to end the incentives of HCT.

So I doubt airlines spend much time pondering the legality or morality of HCT. Though I don't necessarily think it's right, I sure am not going to worry more than the airlines do if someone else thinks it is.