SL: You’re bringing in a bunch of extraneous points irrelevant (and not part of the question or described scenario) to the primary issue of your unreasonable insistence that someone purchase a second empty seat when you don’t insist the same if the seat change request rather than to sit next to the same gender is instead to sit away from a cranky child, sit next to a family member seated elsewhere or to sit closer to the exit to quicker catch a connecting flight.
A seat change request to sit next to a family member, someone of the same gender or away from a cranky child is a normal everyday occurrence in every airport that is equally unobjectionable regardless of any of the aforementioned underlying reasons the customer is making the request.
Yes, I agree you should smile to your neighbors. But that hasn’t to do with the question here.