(Sigh.) It's bad enough that you've chosen to defect; it's downright evil to try to popularize the notion of defecting. The more people do this sort of thing, the more likely it is that Amazon changes their policies, affecting those of us who are co-operating (i.e., not exploiting the policy).
Amazon can take care of itself. It doesn't need your paternalistic moralizing intervention. If Amazon believes that on net having a policy that allows returns of possibly already consumed goods will produce more profit than a more defensive strategy then it can do so. Save your shaming for people who need your defence or who are being 'expolited' in a way that isn't straightforward (albeit miserly) use of the deliberately included features of a powerful website.
Something actually ethical to recommend would be the use of calibre to convert and remove DRM and then returning the book while keeping it. That's clearly illegal and something I incidentally haven't done. I've never bothered looking in to the 'return book' kindle feature for those books I have purchased from amazon. (I just use that tool for the purpose of getting things into a format TextAloud can convert to mp3.)
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.