I always thought the idea of no money was an altruistic Roddenberry-ism that is just not realistic. Holdfast explained it very eloquently, but there simply has to be some sort of value placed on the exchanges of resources and services. I think DS9 did a better job of showing the reality of currency.
I remember watching the episode where we see Sisko working in his fathers restaurant on earth. If there is no money then essentially the food is free, right? What's there to stop someone from just glutting themselves on everything with no restraint? Humans have been greedy and self serving since the dawn of man, is all that supposed to magically go away in just a few hundred years?
I agree. Personally, I think that while there isn't anything that stops someone from doing that, there isn't any huge reason to just chow down anyways. Assuming that this version of earth is post-scarcity, one can chow down on replicated food all one wishes, but they come to restaurants and the like for that extra bit of fresh flavor that replicators can't quite achieve, and to socialize with others. It is a bit unrealistic to beleive that absolutely no one would be selfish, but I'd imagine that in this version of earth, being selfish just doesn't have that strong of a reward.