I'd rather pay an extra $20.00 a ticket than deal with overcrowded over head bins. I used to carry on every time anyway to save about 30 minutes at the baggage claim, but now finding an overhead bin is really difficult unless you're first on the plane.
Of course people have no clue with it either. If they're sitting in the back of the plane, many people stash their big bag in a front overhead bin so they don't have to haul it all the way to the back.
Then there's the people that put everything up there including both bags and a coat, leaving them more leg room, but someone out their bag.
This is done despite flight attendants repeating specifically not to over the loud speaker multiple times as people board.
I have seen a few verbal fights with passengers over the deal, one of which I got involved with after the twerp muttered under his breath that my father was an A-hole after raising a stink that his bag had to get checked because of a purse and coat in his bin nobody would claim.