To Xori:
If you were to treat others how you wanted to be treated, and you wanted to be treated how you wanted to be treated, then would you not treat them how they wanted to be treated given that such treatment does not violate how everyone else wants to be treated, which covers if A wants you to kill B and B doesn't want to be killed.
To the overall conversation:
The Platinum Rule has a single hole in it, and that is that it does not support self preservation. Now given a world where everyone is following it, it should apply fine. But given a world where there are some who do not follow it, the lack of self preservation can lead to self destruction. It is the simple example of the Suckers/Grudgers/Cheaters.