You're giving Harry too much contemplation time relevant to his actions. The whole of Changes takes place in three days. The time from being crippled and becoming Winter Knight happens in three hours tops. It was a move of desperation that Harry could have avoided with less stress and time pressure.
He wasn't planning to break his back, and until that point, though few, he still had options or thought he did. Once he broke his back, he had no good options, being Winter Knight was the least bad. He is stressed up until the time he broke his back, but it didn't include becoming Winter Knight or at least not seriously. So if three days before the fire happened, he had calmly decided to become Winter Knight, and then planned carefully out how he could manipulate Molly, then yeah, he could have saved himself some stress and guilt, but that isn't what happened.
That doesn't mean he was entitled to ask Molly, either.
Of course not, nor is a dying husband entitled to ask his wife to end his pain by assisting his suicide. But it happens, and very often the wife consents to assist. These types of things are not thought out usually before hand, and when it is done it isn't a decision based on morality. There are moral arguments to be made on both sides of the question. Uriel understood that, he also knew that Harry wasn't exactly himself when he asked Molly. Had it been a cold calculated manipulation plan on the part of Harry, I doubt that Uriel would have stepped in at all.
