> This is evil. There is no cost to the airline to put people who booked together next to another. It's seems like Mafia-tactic to seat people apart from another unless they pony up another $500 in upgrades.

The idea is that an airplane needs a certain revenue to run. Suppose it's 10k, and there are 100 passengers. Each passenger thereby pays $100.

However, some passengers (A) wish to sit in a big seat and are willing to pay for it, and others (B) don't care about seat size and are willing to give-up space for a cheaper ticket.

As such, 1 Passenger A may want to pay $250 instead to get a 30% bigger seat, while 3 passengers B give up 10% of their seat size and pay a $50 ticket. The airplane still collects $400 from 4 passengers as before, but the passengers are happier now. They have traded their individual desires, for something less valuable. A desired a bigger seat and thought $150 extra was less valuable than this bigger seat. B desired a $50 cheaper ticket and thought the smaller seat was less valuable. They traded and became happier.

You may say but nah, airlines will simply charge for bigger seats and keep the smaller seats the same price. But they don't, because they must compete with other airlines that don't. If they could do this they would've already.

For seat picking it's the same thing. A prefers to pay to sit close to a friend or partner. B doesn't care and prefers a cheaper ticket. Thus A pays a bit more, B pays a bit less.

I've always had to pay for seating as long as I can remember, I never cared enough (except long international flights), so I enjoy slightly cheaper prices than a world where there was no choice. It's not as evil as it may seem at first glance.