I agree brother fellowservant. Like anything else, there are somethings that need moderation (alcohol, food, even exercising) while others need to be refrained of for good (drugs).
If a man witnesses a nude woman at the beach but does not lust, is he automatically "defiled"? Absolutely not! Its the output of his heart, which is his will and motives that can defile him.
If a man inhaled second hand smoke somewhere in public, is he automatically defiled? No. Of course, its not healthy but he is not defiled. If he purposely smokes cigarettes for example, then he has defiled himself.