Why are smoking and drinking deemed stylish, cool and even sexy in movies?

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In most of R and even PG-13 movies, you can see the stars chaing smoking, and gulping down alcoholics. I am afraid that what triggers plenty of young people to start such habits. Why are such do stars light up and drink so often in moives? And in real life, do they? I would have say no, because they have to exercise, and eat healthy because they have to stay in shape and look good to stay in business.