The Argument of the Two Men

I realize that this argument is at the center of Book two of The Republic but i would like to discuss one specific piece of the argument that i find interesting. The story is purposed by Glaucon in 359d when a shepherd finds a ring that has the potential to make him invisible. He then uses this new found ability to take advantage of the king's wife and take over the thrown by murdering the king himself. Then he changes the situation in saying that now there are two rings that do the same thing, but one is given to a just man and the other is given to an unjust man. Now Glaucon assumes that both would be just with their new found ability because now they would be compelled to act justly by the knowledge of the other individual. This is where i have a problem with the argument of Glaucon. I think that it is very pessimistic to believe that no single individual would have the power to resist the desire to take advantage of their new found ability. Yes, there is an advantage to accountability in the fact that it will hold people true to their word but i completely disagree that no one on earth would be able to resist their desires and temptations simply because they knew that they would receive no repercussions for their actions.