There are a couple of expressions that go around addiction treatment circles, whether for drugs, tobacco or food. One is "there's nothing worse than a recovered addict" and the other is "someone who's never been an addict can't understand." Whether you have been a smoker or have never smoked, you might come off as judgmental or unable to relate if you use a condescending tone.
If you're a former smoker, you've been there and can relate to the need and desire to smoke. You've had the same weakness and enjoyment from cigarettes and are fortunate to be free from the addiction, and successfully overcoming something like an addiction is worth all kinds of praise and re-enforcement. But what works for one person won't necessarily work for another, so keep in mind what you say can sound critical and condescending sometimes. Just don't forget how hard it was to quit.
On the other hand, a person who has never smoked still has some other human weaknesses, so coming from a position of "righteousness" might snowball into finger-pointing and steer away from the real object of scorn: cigarettes.