[chatmasta]

On the other hand, if the user is already leaving the site, is there any reason not to try to bring them back? It seems like a no-lose proposition.

Of course, there is the possibility that the user is not leaving permanently, and your tactics actually convince him that he should. But I assume that the revenue gained from convincing would-be deserters to stay, outweighs the revenue lost by convincing would-be returners to desert.

I base this assumption on the fact that, like you said, all users are not like you. So many websites already employ this tactic, that many users as likely immune to it, or at least ambivalent toward it as a marketing tactic. I doubt most users who are seriously interested in your product would abandon purchase because of a distaste for your marketing tactics (or even that they would harbor such distaste). After all, you can't fault a company for trying to convert as many users as possible. This tactic is so common that if you abandon every product offering using it, you might be left with few high quality products from which to choose.