There are many circumstances where a single person acts for a group. I find it interesting that so many people immediately think of the president of the United States as guiding the direction of our country and having direct influence on our well-being. I think that our individual Senators and Representatives have had a much greater role in creating the economic and social climate we are now experiencing- after all they are the ones that pass the bills and right now, with a liberal majority in both houses they have the ability to over ride the Veto power of our president.
In any group, there are often times that the single person's actions determine the well-being of the group. This happens in the family unit, sports teams, businesses, government and yes, churches. There are many times when talking with a non-believer, they cite the hippocracy of the church leaders as a reason they don't believe.
It's natural to think of the leaders in groups, but Achan wasn't a leader. Often, we have unsung heros quietly working in the background not expecting any recognition who contribute more to the greater good of the group/attitude and direction of the group. These people are just as much that single person acting on behalf of a group as the leader and perceived movers and shakers.