I don't have self-loathing. I simply recognise what I was before I became a Christian. Someone separated from God, someone who could never please Him as I was no matter what good works I thought I was doing. I am far more at peace with myself now and have truly accepted the God has forgiven me for all my sins. I've an assured place in God's Kingdom.
As for the continuing to sin, I still live in a sinful body. It won't become an eternal body until Christ returns and it will change in an instant. Of course I do my best to resist sinning with the help of the Holy Spirit and indeed I am free of some sins thanks to the Holy Spirit, but I am a 'work in progress' as are all Christians. When I sin, I repent of it and am forgiven.
You're also not including the work of Satan and his demons who constantly tempt and taunt humanity in order to get them to sin and fall away from God.
The illustration you give of a perfect kind, good charity worker isn't reality. There is no-one who is perfect, they don't exist. It's at odds with our sinful nature. Go and find me one perfect person.
I think this page gives a very good summary of our sinful nature
https://www.gotquestions.org/sin-nature.html
Unless you can specify the harm they have done in their life, their eternal damnation is simply god's ego driving him to punish them for not believing in him. Can you see this?
Specify the harm done? In countless ways we hurt others. Look back over your own life, honestly. Have you never hurt anyone? Either by saying/doing something you regret or failing to do something you should have done?
People can believe in God and still end up being sent to eternal damnation. It's belief in his Son, Jesus Christ, that is the key, and acceptance that He died for your sins.
If you go by works alone, then at what point should someone be saved? What crime is so bad that you cannot enter Heaven? I'm sure you can think of many. What about lesser crimes? Where do you draw the line, how do you balance the good deeds versus the bad deeds? I think that would be a very unclear and poor system.