I said in my last post that “I don’t wanna” is a perfectly valid argument, and indeed it is. It gets used every single day, lots and lots of times, in all sorts of circumstances. (A good clue, when you’re listening to people explaining why they can’t do something, that you’re really hearing “I don’t wanna” is to listen out for phrases like “I/we just/really think/feel/are convinced that it would be better to/if….” (insert alternative action/inaction of choice). And it works really really well if you’ve got some sort of power to back it up.
That last sentence is a little clue to how things are working out here. If ‘”I don’t wanna” is a stand-in for “It’s not fair on ME”, then it will often be used when the person using it has some sort of nice thing, maybe an unearned advantage, that they don’t want to give up.
(By the way, “I don’t wanna” is not exclusively used in cases of unearned advantage. It’s also used a lot when people have reasons for not wannaing that they don’t really want to fess up to, maybe not even to themselves. “I’m a bit tired to go to the gym tonight, I’ll go tomorrow”, “I need some time to think about that difficult report so I’ll start writing it tomorrow” and “I could wear those trousers with lots of other things in my wardrobe so it makes sense to buy them” are all examples of “I don’t wanna” in action.)