Put yourselves in a drug dealers shoes. If some old guy who you don't know starts talking down to you about how bad drug dealing is are you gonna say, "You know what, he's right, I'm gonna turn my life around right now" or are you gonna say "Who the f*ck does this guy think he is" and continue doing what your doing. By talking down to people he's made this into 'me vs. you' instead of the much more effective let's work together to solve this problem. It's effectively become a zero-sum game.
He'd do much better if he took a more collaborative approach where he says "You stop selling drugs and I'll use my credibility to get you a better alternative". This way it's win-win and much more effective.