I'm assuming the airline gets paid the full amount for point A to B. If that's not the case, and they do end up losing money (i.e. due to a refund), then I can completely understand their perspective.

I agree that it's an expectation that someone would want to complete a trip that they paid for, but not an obligation. The only obligation in this contract is that the airline take the passenger to the destination they paid for safely and efficiently. For the passenger, provided they are behaved, there are no obligations to even be on the flight!

The airline should have no legal authority or right to detain someone who they suspect is skiplagging, but I agree that declining the sale of future tickets is entirely within their right. You break their policy (not the law), and they decide on how to follow up. That's the risk of skip lagging, but the airline in this case even forced the kid to buy another ticket!

I’ve also been in the position where, due to the airline’s ineptitude, I elected to ditch a short delayed flight and make my own way home. When this happens, it’s essential that you tell the airline. They will be much more understanding when it happens due to their unplanned schedule changes.

You go above and beyond your obligations to the airline! But I respect that you're honest with them when it happens.