Ah, another arbitrarily-chosen end to the personal responsibility train. These are popular, no doubt, but you don’t see this particular model around these parts too often.
So, the responsibility for horrible crimes committed by producers and distributors of illegal drugs falls to the end users due to their choice to indirectly finance these endeavors. This transfer of responsibility stops, however, at the user level; decisions of others, such as jebert, to indirectly finance these indirect financiers do not continue to transfer responsibility. (Whether any responsibility for their own actions remains with the people further up the chain from the end user is an exercise left to the reader.)
By any chance, do you care to present a logical rule system to determine where responsibility for an action can and cannot be transferred via money, that’s cross-applicable to other situations and produces this result? Or is it simply that responsibility for any action continues to transfer until the next step in the chain would be inconvenient for you personally?