And then again, according to this article in Discover, they might not. Check the comments to see the counter-research, as well as ever-more skirmishes in the ongoing American culture-wars.
To the extent that graphic warnings don’t discourage smokers, I’ll rack this up as one of the many many many counter-intuitive things scientists have discovered about human beings.
When the original cancer warning was required on cigarettes, the tobacco companies initially fought it tooth and nail, but after the law went into effect, their sales actually increased.
Maybe smokers interpreted the warning as "The Man" telling them what to do, maybe they rationalized from a gamblers viewpoint, each thinking he would be the lucky one, maybe they were simply in denial.
In any case, I suspect much research was done by private sector marketing firms to understanding this quirk of social psychology to sell stuff.