A building maintenance guy once told me the following story. He went in for a maintenance call. A couple were sitting on the couch, high out of their mind. He heard a baby screaming. Went over, and saw the baby screaming. Figured it had a wet diaper. Found the diaper stuck to the baby's skin, and a cockroach crawled out. The skin had grown onto the diaper. He immediately called the police and the parents were arrested.
People on HN pretend like every drug user is a high functioning recreational user. In reality, drugs are addictive and destroy tons of lives, including those of many people who are around the drug users.
Now, I agree that the costs of enforcement outweigh the social cost of drug use. But it's not totally irrational to feel otherwise.