Speaking as one who has used heroin and who currently smokes a fair deal, even trying to compare the two is like.. eh. Trying to compare a very mild paper-cut with the severance of a limb. You really can't.
If you're really going to go down the 'you're fucking up your life by smoking' route, where the hell are you going to stop? Banning fat people from eating cake, forcing abortions on teenage girls because they're certainly fucking their lives up by getting pregnant too early, legislating on what education people take (and I mean choosing someone's career path for them based on perceived strength, not saying your populace need to gain a basic level of education before leaving school), choosing what people read, say, and do in case they fuck up their lives by doing so? Prosecuting people for being in destructive relationships, fining people for dying their hair a stupid colour or getting visible tats/face piercings (since that seriously hinders possible career choices, and therefore fucks your life up to a degree)?
Where exactly do you stop on this slope? Seems pretty damn slippery to me.
I actually sort of outlined that.
You stop when people DONT hurt other people around them. A fat person eating cake ONLY hurts himself. Smoking of any kind produces second hand Smoke, Polution, etc. Thats the difference between Drugs and cake children. I would consider smoking a form of manslaughter if I had the choice.
Cigarettes and the drugs in question ARE similar, you cant deny that. People fuck their lives up from smoking AND heroin alike, you dont need to have done either to know that.