Chemical addiction is not comparable to overeating/lack of exercise. You could theoretically be "addicted" to McDonalds and still live a fairly healthy and balanced life in other respects. It's really not possible to be addicted to heroine and live a balanced lifestyle. Even though drug addicts are largely personally responsible for their actions, that doesn't make it less true that drug dealers are knowingly profiting off of vulnerable individuals and actively encourage them to ruin their lives.