I'm guessing you have never struggled with nicotine addiction, or perhaps you're one of those people who experiences a more mild addiction than average. But if

I'm guessing you have never struggled with nicotine addiction, or perhaps you're one of those people who experiences a more mild addiction than average. But if most people were to develop nicotine addiction for several years and then stop for a week, they would experience mental anguish far beyond what anyone could consider "healthy". For long time smokers, that anguish can go on for months. Healthy people do not experience intense mental suffering simply because they don't have nicotine. It's a disease - an illness - even if it does not cause cancer.