I believe the integration with the drug trade started as a way to fund CIA operations.  In the early days, Dulles and crew discovered they could do amazing things (like overthrow Mossadegh in Iran) with very little money.  What could they do with more money? Trouble was, their budget was capped through Congress.  So they found other ways to do things to raise money that they might have even thought were patriotic and in the national interest (like getting involved with arms trafficking, drug trafficking and probably even human trafficking).  At some point, when they end up taking out a President in order to keep their secrets, they had definitely crossed a line.