I know that they want to "fill every seat."
If you take this LITERALLY, then you'd want to overbook, because of the statistical percentage of "no shows." That, of course, leads to "bumping" when more passengers actually show up than the statistical formulas predict.
But one could also define "fill every seat" as "sell every ticket," then there's no point in overbooking. From an economic point of view, a seat would be "filled" as soon as the ticket was sold. Whether or not the passenger showed up wouldn't be of concern, as long as the ticket was paid for. And if a passenger wanted to change flights, s/he could be charged a penalty to cover the expected loss on the replacement; the closer to flight time, the higher the penalty.
A "full" plane is a crowded plane and thus an unpleasant plane. A plane in which every ticket was sold, but there were a few "no shows" is actually nicer to ride on. It would also be easier on the plane; there would be a smaller load.
Can airlines be persuaded to change their objectives in passengers' favour, so there is no "bumping" and less crowding? Would it make sense for passengers to push airlines to adopt other solutions (such as charging 10%-20% more for tickets, to compensate for the lost "overbooking" option). Would this (or some other idea) be better than forcing passengers to buy first class tickets if they want to avoid being "bumped?"