On the Sith Lord topic, just once more. Leading up to it, Anakin found out he was really the Sith Lord. He turned his light saber on him, he could have killed him but instead he turned him over to the other Jedi. Now you can argue he didn't kill him because he said he could save the love of his life. He still turned him in.
No one could have imagined the troopers were going to turn on the Jedi or everything that had passed. Before he tried to kill the Sith Lord. Anakin was saying "No, It's not the Jedi way" right before he defended him at the last moment.
I just feel the only reason he did what he did, in his mind he believed the Jedi had turned against him and even at the end of Revenge of the Sith he said something to effect "I believe Jedi are evil" and he replied "Then you are lost" you have to admit, it was pretty dark side to kill a man while he was down regardless of how evil he was.
Doing that is path to Dark Side...isn't it?
Yes, it would have been a Dark Side decision (in game mechanics), Mace Windu would have broken the rules and act against the Jedi way. He thought that Plapatine was to dangerous, to keep him alive as he should as a Jedi.
If he would have done it, I think he would have been removed from the council.
A similar RL situation would be:
A terrorist has placed a bomb which could kill hundreds. It will blow up after a certain time and only he knows where it is. It is against law and human rights to torture him to find out. But there are at least some policemen who wound do it.