Writing is a LOT of my job, so it comes somewhat easily...sorta. I have always been able to write out my thoughts better than speak them. But then I also speak for a living so...(Are you able to write your long posts just as they appear here, or do you spend hours writing and rewriting, like I do? I'm so glad I don't do this for a living. I'd never get paid.)

Totally-I now have no need to feel guilty for past sin, because it's water under the bridge (rather, blood on the cross!)

- sorta, but it is dependent. Jesus did what He did, no way I can change that. But I can ignore it. I can choose to sin without repenting, and then "there remains no more sacrifice for sin."and my future sins were all paid for at the same time,
There will be "sons of God" in hell. It is their choice to be there. "as a dog returns to it's vomit..." God wants relationship with His children. But He cannot abide alongside sin. I tend to equate those two things - Fellowship IS relationship.But to maintain my fellowship with God (NOT my relationship--that is fixed,) I need to keep the way clear between us.
We do not have to be perfect. But I do think we are expected to exert a "perfect" - meaning complete - effort. But even when we fail to do even that, God is merciful if we seek His mercy. And I do believe, to some extent, He overlooks our recklessness - as a father overlooks some of the reckless behavior that teaches. However, if we choose to leave the house and go party in the pig pen, He will not come dragging us out. He will however run to meet us and restore us when we choose to be restored. The "coming to himself" of the prodigal was guilt driven self-examination and awareness that the worst of what he left behind being better than anything he thought he was going to get, and ended up getting. His guilt gave way to repentance, and the father more than welcomed him back home. It is a story to remind the sinner that their guilt is not a reason to stay away, but a reason to turn to God for it's relief. Submit and humble yourself in the sight of the Lord and He will lift you up. I feel guilty when I choose to act against my own convictions toward the Lord to live otherwise.
Perhaps, the over-riding feelings of guilt and helplessness, the misplaced guilt that paralyses and drives one deeper into sin, could somewhat be the result of an incomplete vision of God the father? That's also a much deeper subject for another time...