Earlier quoted context omitted.
They are the scum of the universe. If you don't pay for your seats, they will separate you and your party even if there are available seats together, because they know you'll shell out cash to fix it. (I think American does this now too, and possibly others but I haven't confirmed they also do it when there's available seats).
I'm actually fairly upset when airlines _don't_ do this. They're just leaving money on the table. If you want to pick your seat, pay for it.
Ya its called a ticket, which are typically received in exchange for money. Should airlines also charge a disembarking fee? pay up or don't get off the plane? Seems like that's more money left on the table, captive audience and all.