Interesting. In your question, you let me choose anyone but the drug user to bare the responsibility. Why is that?
To illustrate a truth by using an absurd, false choice. Of course the drug user should bare the responsibility. Libertarian policies would reward the drug user by decriminalizing to legalizing his activities, and punish all those associated with him by magnifying the societal damage done by unchecked, undiscouraged, drug trafficking and usage.