If I'm leading someone down a section of river I do all that I can to adequately explain the hazards of that said river. In situations like the one above, I would make the boater scout the rapid and make his own decision on whether or not to run the rapid. If you are blue angel'ing down a section of river and you are not telling people that there is a significant chance of drowning if you go left, then you are somewhat in a grey area.

For example, if I lead a group down section IV for the first time, and I don't explain anything to them, do I get in trouble if they go right at Crack in the Rock and die? I think so.. But that's just my opinion.

I have no idea what happened on the Blackwater, but it sounds like someone may or may not have been adequately informed about a section of river that was really dangerous. If he was, and his death is due to a lack of skill, then that is a totally different scenario.