SE seems to be trying to combat a phenomenon called
diffusion of responsibility. YES, it's difficult for any one person to meaningfully contribute to the giant honking mansion. However, if you guys can't trust people in your FC enough to donate a small amount (500k-1M, which is not large) to a common cause, then there's a problem. The other problem is that everyone assumes they're going to get the highest quality largest size mansion, when that mansion is designed for super large FCs. OF COURSE it's unreasonable for a 50 person FC to get the giant-ass mansion because it's designed to be bought by 100+ people.
I'm not in their FC but I like hanging out in TS3 with Pass the Bong (the largest FC on my server) and yesterday I heard them all banding together
as a group to brainstorm ways to make money and then they went and got it. Obviously, it's a long, hard, three month project to raise 312M to get the big-ass house but they sound committed and it's giving them a cause and a goal to rally around.
If a bunch of stoners can summon the effort to make 312 million gil, why can't you?