Just because some people won’t buy anything that isn’t on a coupon doesn’t mean coupons are bad.
Because you can save money by getting a cheaper flight by understanding how pricing works and adapting your purchasing strategy. Many consumer are willing to spend time and effort getting a better deal.
This can be true even if the lower price is nominally a discount. Before everybody would pay $100. Now you can pay $80 by screwing around but have to pay $150 otherwise, and the screwing around is $40 worth of inconvenience. $40 is less than the $70 difference between $80 and $150, but $80 plus a $40 inconvenience is a higher cost than the original $100 uniform price, and obviously so is $150.
Which is bad for consumers and the broader economy.