Whilst I agree that this topic has been debated to death in the past on these forums, I would just like to point out that the commercial situation is subject to the increasing proportion of non-refundable tickets being issued per flight. The reason why LCCs do not overbook is that they generally have all tickets non-refundable; to book more than the total number of flight seats on that basis would be tantamount to fraud IMHO.
As "normal" carriers increase the percentage of non-refundables in their mix, then this needs to be taken into account in their over-booking algorithm. As a pax I would be more than annoyed if I turned up on time for a flight with a non-refundable ticket and was refused boarding. In fact this very thing happened to me a year ago on a ferry in Scotland, and I and the other pax affected were able successfully to convince the operator that it had a legal obligation to find and operate an additional vessel to get us back to the mainland there and then, which is precisely what it did!