So far I haven't witnessed a Bash crash, so I can't say what caused any of them specifically. However, I have been in plenty of group rides, and have seen how they could go wrong. It seems that large group rides involving sport bikes can be broken down into a few segments of riders.
First, you have riders who are fast and have the ability to leave the majority of the group behind without creating a dangerous situation.
Then you have the guys who, for whatever reason, are slower members of the group. Maybe they just aren't as skilled at higher speed riding, or maybe they aren't familiar with the road and just want to be cautious. Not a problem here at all.
The next two groups are where you begin to have issues...
You have riders who just can't stand to ride within their skill level on the given road. Maybe it's because of adrenaline, or because they can't bear the thought of being one of the slower guys. Whether it's out of ignorance or some sort of macho thing, these guys are riding beyond their skill level and put themselves and the rest of the group at great risk.
Then you have the riders who might be new to the bike or new to riding in general, and may be afraid of holding the group back. These riders may unknowingly put themselves and others in an unsafe situation by trying to keep up instead of riding their own ride.
It seems to me that these different groups are more clearly defined among sport bikers than with other types of motorcycles. 99.9% of the time, our speed is limited by the rider's ability rather than the limitations of the machine. That is not always the case with other motorcycles, where you run into lower limits of things like lean angle, horsepower, and braking ability. Those factors tend to help level the playing field for cruisers and the like. With us, it's all about honestly evaluating your skill level and abilities, and not riding outside of those limits.
If everyone can be honest with themselves about what they can safely do on their given machine, all will be well. The faster riders won't mind waiting a few minutes at the next stop, and the slower riders shouldn't mind taking a few extra minutes to get there.
If we can't manage to do this, then I think smaller groups like we typically do now are the safer way to go.