I believe the dangers of group riding simply boil down to the primitive instinct to keep up with the herd. You don't want to fall behind, nor do you want to slow up the riders behind you. It's easy to say "ride your own ride", but that's rarely going to happen when you're caught up in the moment. Throw in a machine that's constantly taunting you to give it it's head, and it's no wonder we read and hear about all of the accidents involved with the group ride.
A possible solution, clearly define the kind of ride your group is going to have. This should be based upon posted speed limits. The group is either going to ride the speed limit, or it's going to exceed it in various increments. Now, at least you know what you're getting yourself into. My two cents.