The average WDW CM is probably not going to have an "alpha" personality. They are going to be intimidated by these large groups when they begin acting in unison. Whether it is their job or not, it is asking a lot of someone in that position to confront a group like this when they are breaking the rules. Managers and supervisors should be expected to do so, but I wouldn't expect the average CM to intervene.
IMO, CMs should be able to ask for help from a supervisor in these situations without having to get involved directly. This would probably keep them from just walking in the other direction when they see it happening. If you want policies to be successfully implemented, you have to consider things like this.