Drugs cause a lot of collateral damage to friends, family, and society, so it is reasonable to treat them differently than, say, extremely spicy peppers.
Making it illegal also causes collateral damage. Drug gangs, taxpayer money spent on jails and enforcement, deaths due to fentanyl lacing, spread of disease due to needle sharing, foregone taxation revenue, incentive for petty theft, adoption of worse but cheaper substitutes (crack cocaine, krokodil).