That is certainly the common wisdom. As is throwing away return legs if a round-trip is cheaper. I've done it at various times for various good reasons--mostly changes in plans. And I doubt anyone is going to get banned for doing it now and then. But if you do it every week? Maybe.
It's probably not even so much because of overselling which I don't see a lot of these days at least where and when I fly. But, if travel goes sideways because of weather/mechanical issues/etc., as far as the airline is concerned it's the ultimate destination it needs to get you to.