Most people are two-faced. They buy deeply-discounted non-refundable cheap tickets but then have a flat tire on the way to the airport (or some other lame excuse) and miss their flight, then the little snowflakes kick/scream/cry/demand seats on the next flight.
Who pays for the missed flight's empty seats? (Yah, I know. The snowflakes expect the airline to absorb the loss.)
The primary reason airlines overbook in the first place is because of irresponsible/late/no-show people that can't plan well enough to make it to the airport on time.