I halfway disagree on this one.
While I agree that an organizer has some level responsibility to provide a safe venue for his or her event, at the same time EVERYONE in the backcountry has a personal responsibility for their own safety. That's why we call it the backcountry, its one of the few places in todays world that we get to make our own decisions. We don't have some idiot in the gov telling us what we can and cannot do in the backcountry and we would really like to keep it that way.
Plus, the last time I checked there is no super qualification required to be an event organizer, just a passion and enthusiasm for the activity, so why we would look at the organizer as the keeper of all knowledge and safety is beyond me. Its the BACKCOUNTRY, just because someone doesn't tell you to get away from the edge of the cliff or the bottom of the hill does not mean that its safe or prudent to be there. Everyone at that event had access to avalanche reports that were screaming danger danger, and everyone knew how much fresh snow had fallen recently on a suspect snowpack. If they didn't know those things then they had no business being anywhere near the mtns. Our society is already like a bunch of sheep that blindly follow each other around, please do not further that unfortunate trend by placing all the blame on the event organizer.
Yes, it would've been prudent to restrict one rider to the hill at a time, or to postpone due to conditions, or perhaps to move to a safer location. But no one was forced to be there, and I'm not even sure anyone was paying for the privilege to be there, the backcountry comes with inherit individual responsibilities, please do not try to pawn those responsibilities off on some organization or gov branch.
I am truly sorry for the victims, and especially sorry for their families. May God be with them and may they all receive all the support and love they need to get through these trying times.