One, there isn’t. One party undercutting another for the same product is how competition generates consumer surplus.

Two, it isn’t the same product. When I fly with my family, we check in together. We board together. I collect their docs on my phone and double check they have them on theirs. I turn down upgrades so I can sit with them. If there is a change, it takes one customer service agent maybe 10% longer to adjust everyone in bulk. I’m not incurring 4 or 5x the cost on the airline for 4 to 5x the revenue, this is why bulk discounting exists for everything.

This isn’t an ethical problem. If it’s triggering an ethical system, that’s more damning for the system than for Delta. This is a communication and brand problem.