I believe that the person abusing the substances is trying to connect to something--to fill a void--but they only create a wider chasm. They separate themselves from other people as well as God. It's not just drugs that do this. Any excess can be harmful. There is a Bible verse that says that all things are permissible but not all things are beneficial. That's why the drugs are not the problem--it's the misuse of the drugs that is the problem.