Consider an analogy: if someone went up to Oskar Schindler and said "I know you are helping Jews escape; if you don't pay me $150k I will tell the Nazis about it", don't you think Schindler had the right to prevent that person from making that known - even if the only way to do so was murder?
Selling people drugs for profit is analogous to freely saving people from Nazi death camps at considerable risk to your own life?
If he did this, it seems very naive to think it was to save all those poor druggies from exposure, rather than to save his own profitable site.