What a long (and complicated) thread to read... So here's my contribution to this subject.
Going back to the original OP, the 2 players are masters of logic (and both love beer). They want to maximize the number of beers, they don't look to get more than each other. The word "sucker" will not affect their judgements either (emotional triggers do not affect masters of logic). In that case defecting would be stupid, illogical and an EMOTIONAL decision.
That being said, Masters of logic would always cooperate. Defecting even once is an emotional decision
Now I realize that, since this thread is taking so long, people are considering these masters of logic as regular people with feelings, who may seek EGO results and even vengeance.
Well, in that case, NOTHING BIG really changes either. The only chance of defecting would be at the last round (unless these masters of logic are plain stupid). If that round is defined before hand, they may both defect or both cooperate that round and the total number of beers they accumulated will change by a maximum of 1 beer.
Now if we don't take the "masters of logic" part literally, we will end up in what the humanity has been through since early history. And one of the 2 brothers will kill the second to maximize its winnings and wealth. We may even find a World War I or II scenario. In real life, this game will never end. People will end (being mortal), but the game won't, it will continue with our children and grand-children playing it.
That is why now we know that our decisions are much more emotional than rational, and some people (egoistic, short-term people), may at some point choose to defect.
I assume that this puzzle may have something to do with the situation the world is right now. And if you don't know what I'm talking about, just watch the news.
I don't intend to discuss politics, I hate this subject (everybody assumes they are on the "right" side of the conflict). But in my opinion, the intention behind the United Nations was to provide an arena for this game to be played rationally. (My opinion about the UN set aside).
Remember this: "We decide emotionally, then justify it rationally!"
In 2 words, No one wil be sober after that game ends