From what I know, [attorney-client privilege] is the only place in the States where confessions are really safe.

That's assuming you have an attorney who is honorable and follows the rules and doesn't make mistakes.

If an attorney broke privilege to prevent some bomb from killing 100 people, you can be sure he'd be hailed as a hero, not face any real consequences. And for a case like that, I'm not even sure the privilege is absolute.

But research ethics don't apply uniformly to all illegal acts. I think researchers can study people who are using drugs illegally but can offer them confidentiality.