I like the idea of posting warnings on triggers in media.
Gone, Baby, Gone did make me uncomfortable, and I know the scene you're talking about. I like the way the movie played out, though. You think it's a movie about one thing, and it turns out to be a philosophical question. The way the Casey Affleck character at the end sticks by his convictions was impressive, I thought.
That said, if anyone wants to watch the film, just skip the scene where the cops and Affleck are going into the house with the three drug users.