It's not an mlm scheme. It's people delivering a product where there is demand for it. The only countries that have limited drug use are the ones with excessive penalties, laws that are extremely unpopular in pretty much all of the western world. Another poster in this thread also high lights some of the issues with those laws.

Your also making the assumption that drug use it self is a problem that needs to be solved. But it's not, lack of access to clean drugs and lack of support system for people with issues is the problem to solve.