
A lot of what I did pre-ROTS had to deal with why Vader thought himself irredeemable. I always remembered that he had been the one to betray and murder the Jedi and, admittedly, wrote extensively about the Purges and the fall of the Republic just to sate my personal creative curiosity. I also had a fascination, as I'm sure most fanfic authors did leading up to the PT, with how Padme would "pop her clogs" as they say in the British Harry Potter editions. In one version, I actually got it right with a Force-choke. In another, she and Vader dueled to the death with Anakin and Vader's lightsabers. I also had one idea going that I've used several times where she had a degenerative heart condition so that she died when Leia was two years old. I just couldn't make up my mind.
One thing for certain, though, was the idea that, whatever happened in the Purges or in terms of her death, Vader would blame himself. That's what I read into the "It is too late for me, son." I didn't think that line had anything to do specifically with Vader's hate, but it had so much to do with his guilt at failing both the woman he loved and the son he never knew and abusing the both of them. Hate had contributed to it, which is why he uttered that statement of defeat just after Luke's comment. I think part of why he saved Luke in the end was the fact that he finally realized that he wasn't completely made helpless by the force of his anger. It was kind of a paradox that in seeking the power of the dark side, he made himself so utterly weak and conflicted.
Now, however, after seeing ROTS, there's a new dynamic to consider. You all remember the slaughter of the younglings that is only implied, but that we know happened thanks to some brilliant writing on our friend George's part. (Obi-Wan and Yoda's trek among all those dead bodies and Yoda's line about the padawan being killed "by a lightsaber, was" had me actually crying. And then we got to the scene with Obi-Wan looking away from Padme's very pregnant self and having to tell her that he saw a recording of him "...Killing Younglings" as if it's the hardest thing he's ever had to confess on someone else's behalf. That nearly broke me. Call me a sentimentalist, but not to my face.) It is the one place in ROTS where Anakin's resolve visibly falters and you know that there's a part of him in there that is rationalizing that he is doing this to save his wife and child, but that his wife and child do not deserve a child-murderer. You also have to think that he might have been wondering if he could have done this if his son were among those cowering behind the Council chairs. That's why I love the hesitation so much.
So, why does he consider himself irredeemable? Is it because he has failed at every turn? Does he still remember the younglings' terror when Luke comes to him, trusting him to save his life when the time comes?