I'm not sure you can blame today's events on the fans. You chop off 6K of the route and naturally all the people that were camped out there waiting are going to relocate to the end of the newly reduced course. There was only so much space on the shoulders of the road. Expecting that many people jammed in to that little space to not cause a problem seems a bit unreasonable.
That's not to say we won't find out that one idiot caused the whole thing -- just that it was a nearly inevitable result.
I don't entirely blame the organizers either. It sounds like truncating the route was the only reasonable thing to do. I don't know what the answer is, but the problems are obvious.