A more accurate analogy would be if someone sold me a ticket to swim in their pool, then as soon as I show up and start swimming in their pool (having already paid for the ticket to swim), they say "actually my brother wants to swim" and call the cops when I don't want to leave because I haven't got the swim I paid for yet.

Except that's still not a good analogy because that involves the personal property of a discrete individual, not the somewhat public service vehicle of a faceless corporation. We shouldn't allow corporations to run roughshod over the little man. Just because civil suits exist as a potential route for renumeration doesn't mean we should allow this behavior from airlines in the first place.