You know what's the most interesting part of this whole debate? If you read the "Making of Episode III" book, originally, Lucas conceived, wrote, and shot Anakin's turn in the manner to which you suggested. But, he didn't think it jived with what had been done on Episodes I and II.
Plus, he really wanted to show that Anakin, even by choice, was a victim in this whole game. He did choose, but between the Jedi and Palpatine, he was also a victim.
And I can understand the idea of "Darth Vader being a victim" would piss off Original Trilogy fans.