I totally get you being on a moral crossroads when it comes to do these kind of things.
You know what really helps me when I am faced with these kind of feelings, is just remembering that everyone has their own path in life.
This doesn't mean that you should enable or even support him but just being honest about how you think of it and telling him that in the most respectful way you can.
Or atleast, that's what I do.
A good friend of mine is a pretty big drug dealer.
I know everything.
And I just tell him how he has chosen this path and it's up to him to deal with the consequences but I in no way will enable him (he has asked me to help him shift his stuff).
:)
Just sharing my lil story here haha