Ghost has been "trying to go clean" since S1E1 and epically failing at every turn. He simply can't go 100% clean.

BTW in case you haven't noticed, most of the show's characters are dead. Almost all through brutal murders.

I don't think it's particularly edgy or controversial to think that in the end they all die and the final shot is Ghost looking at the sky right after he is nominated as Lt. Governor, after being shot by Tariq (who subsequently is shot by the police, fitting) wondering what might have been. I actually think it would be b.s. if basically everyone in the show dies or fails and Ghost "makes it out" and becomes a politician. With his past? Give me a break.