It's an interesting moral question; there are definitely shades of grey.

The way I've always seen this analogy is that if your going back every year and breaking a leg then, clearly, there is less and less moral obligation to fix it for you (beyond setting it etc.) so that you can ski again.

Or in other words: if you find over and over again you can't ski (by breaking a leg) refusing to take the hint should be discouraged :D

Now lets take obesity; if someone thinks medical work will help them get healthy again then fair enough (it could even be the piece of phsycology needed to fix their attitude if the problem proves to be non-medically caused). But if they are back in 12 months time with the same problem then there is the same lowering of moral imperative to provide help. If nothing else it is likely a temporary solution again and, so, other forms of treatment/help should be encouraged (I'd even argue it is morally better to suggest other ideas first in such circumstances)

(I'm using the royal you btw :))