: Another major problem is that you (we) would have knowledge that we should not have. Imagine how Gandal,Elrond etc. would react to some stranger who know just as much, if not more, than they did. I wouldn't want to find myself in that position, would you?

That would be great. Imagine the expression on Gandalf's face when you would say: " Hey Olorin, let me try that Narya, so that
I can defeat the Balrog in Moria". Of course You would probably be dead before you finished the sentence.