If you haven't figured it out yet, smokers are foolish addicts, just like drug addicts and alcohol addicts. Nothing you can possibly say will ever convince them to stop their addiction.
Like every addict, feeding their addiction is more important than anything else in their lives, and I mean EVERYTHING. No meaningful and polite nudging will convince them to kick their habit. They'll have to finally make that decision themselves, and usually after they've suffered some type of adverse consequence from their addictive behavior.
Being fools to ever get started, the only intervention that "may" work to convince smokers to quit is direct, in-your-face, confrontational intervention - something like ninja therapy.