On the other hand, what to do if some people don't act responsibly and get addicted; and then for instance ruin their health or neglect their children. Who should be responsible for helping them go to rehab, fixing their health problems or helping their children? If it means the society has to take care of this, then isn't it also fair that society tries to prevent people from getting addicted in the first place? And prohibiting drugs is one way of trying to do that.