All true, but I don't think all or even most of the participants in those type of rides are professionals of that sort.

IMO it's pack behavior, no more, no less. Get enough people together, get the adrenaline and testosterone flowing (yes in the women too) which happens any time you have a competitive athletic group, and the pack mentality takes over. Those who are not a member of our pack are undeserving of consideration. Those who are not a member of any pack, less.