I was struck by this line as well when I first heard it in the movie, as not very many lines of that caliber (as in thought-provoking) appear in the "newer" movies. This is a line written in the film to show how far Anakin had really gone. Obi-wan was really the only Jedi at the end who still supported Anakin, and still listened to him when he was angry about being rejected from the title of Jedi Master. The council had for the most part distanced themselves from him.
If you think about it, the Sith are portrayed for the most part as cold-blooded, robotic beings, fueled only by their desire for power, power and more power. The line referring to Anakin's new vision of everything as black and white meant he was losing touch with his human feelings and therefore reality. Cold hard logic: if I join Palpatine, I will be able to prevent Padme's death, regardless of anything else that might happen because of this!
This is further evidenced in the fight between the two Jedi, Obi-wan and Anakin where Obi-wan states:
"I have the high-ground Anakin"-Obiwan "you have no idea how powerful I have become!"-Anakin
At which point he, meaning Anakin, loses many of his appendages.
Darth Vader had become so heartless that he did not even calculate the danger of his body being injured by attacking at point.
And anyways, what if I said everything I have said is a lie?