By the same token, if you friend can control his expenditure and lust over the hobby (hey, don't expect him to stop upon acquiring the camera body!) and still spend sufficient quality with the family, then I'd certainly encourage him! It'll gonna be a win-win. Fyi, contrary to common beliefs, I have actually successfully discouraged some of my friends from picking up photography! :devil:
The DSLR can be an incentive to stop smoking, then once he/she gets enough money to buy the DSLR, it should be long enough for him/her not to touch another ciggie again.
... If he/she is determined enough, that is.
I'll vote "NO". He should quit smoking NOT because he can get a DSLR as a result, but because he knows it'll be good for him, good for his loved ones around him, and good for his children (if he has any).