I can't figure it out how they know how deadly smoking is and they still go ahead to get more. You're right, the negative effect smoking has in their (smokers) body has never been a problem to them, is like when ever they don't take at least 1 cigarette it makes them go mad. Some say when they take cigarette it makes them to think far beyond human reasoning, like they see things non-smokers don't.
One of my neighbor continued smoking even when he's feeling sick, some don't care and they know their faith, they smoke they'll die they don't smoke they'll still die so why stop when you're sick? Life is all about the decision we take.
That information on cigarettes packs (smokers are liable to die young) is one of the best advise the producers have to give to their customers and they know how harmful it is to their health (which means, take but don't abuse it) but some if not all customers do ignore it, right from when I was little it has been there but smokers do take it like it's a life saver.
That warning (smokers are liable to die young) doesn't signify that they'd stop after a particular rounds is just like the producers of cigarettes are letting the public know that they're never responsible if anything goes wrong, that the customers have to take but take it responsibly.
You're right that people's life are determined by God but that doesn't mean that we should use our own hands to kill ourself. Smoking isn't bad but when is excess that's when it's bad, honestly people don't care how it all end up for them, if someone who's a smoker who knows his gauge (maybe one or two sticks of cigarettes) and he's tell another smoker that if he takes too much of cigarettes that it will affect his lungs, the other one can say he (the one giving the advise) is too scared or hasn't gotten to that stage of taking more than 2 packs at ones, so some smokers are the cause of their problem.