DaasYochid- Your comparison to sugar and smoking,
in my opinion is absurd.
Smoking is very, very dangerous and even if you quit right away it could still have an effect on you later in life. Eating candy all day is certainly not as terrible as the effect of smoking. That is besides the fact that smoking is addictive. Even Rav Moshe tz”l says clearly it is assur to get addicted. Also, the dangers were not as known back then as they are today.
{NOTE:I do not mean that eating candy all day is not bad and terrible for your health, but I think that it does not touch base to the terrible sakanah one puts himself into by smoking}