Although there were (and are) Dons who proscribed drug dealing, different Dons go to different extents to proscribe it or discourage it. However, they tend to show their real hand when it comes to profiting from it endangering them. I thought it interesting that while Vito told Sollozzo that drugs is a dirty business, his primary objection to becoming involved in it wa the danger it posed to his other criminal activities. Of course, it shold be noted that Vito had no objection to how a man makes his living.