Yeah, rules are extremely important. We actually have another side of the problem: often people may just take off because they see the straight pass, so they consider it to be fun. Not so much fun for others especially if not everyone is a great rider. I hear stories all the time about people falling off because of these "fly away". So for me rule #1 is to ride as fast as the least experience rider can handle (or separate in 2 groups if someone wants to ride faster).
I have greenies, so I always try to choose carefully who I ride with, and not too many riders in group. Accidents happen, you know. Plus one of my horses is a kicker, so she REQUIRES others in nasty way to have her space and not bother her or me. However I noticed people are pretty ignorant even about the warning or red ribbon and still try to pass you on higher speed or tailgate you from behind. I had her kicking horses in sides several times, so now I mostly ride by myself - just much easier on both of us (I don't have to be under pressure to track her each movement and ears position for the mood).