Actually, it's often quite a potent form of encouragement, lesson teaching, to show someone rather than tell them. There are times when it is necessary to talk, and times when it is necessary to teach by example. I'd imagine they developed this line of informing the masses because there are so many parents that smoke profusely whilst preaching at their children not to do the same. "I can smoke because I am older than you, and you have to listen to me because I've authority over your actions", is generally pretty ineffective. There is also the idea that the younger siblings idolizing the older will adopt their habits, which actually is the case a lot of the time (though not always).

While it's very easy to criticize, there is some merit to all of this campaigning. If it stops one kid from wasting money on cigarettes, filling their lungs with crap, then I guess it's worth it.

note: I just thought I'd present a different perspective on the matter.