"Jesus says that God takes what is not rightly his, and reaps what he didn't sow." you said. You're a bit biased to be asking a question.
Everything is rightfully God's and God can reap everything because God's sown everything.
Humans aren't the ones to do the forgiving. God either will or won't do forgive and will decide who is unforgivable, not mankind.
Haven't you ever done something wrong? And if you have wronged somebody else but are truly remorseful and regretful over what you did, it's fair for them to forgive you if they can find it in their heart to do so. If you are unrepentant, why should you be forgiven by those you've wronged? If you are unrepentant, you still bear the guilt of your crime and you would just as quickly do the same thing again.
I have to say, I don't believe that an Atheist who puts every bit of effort in to making the world a truly better place, helping the homeless and those who are vulnerable etc. would go to Hell. I don't care which scripture you quote.
There's that quote:
I am the truth, the life and the way and nobody comes to God but by me.
An Atheist who dedicates their life to doing good without seeking reward or personal gains comes very close to being a Christian - even if they don't really pray or particularly believe there is a God.
Whereas a Christian that does nothing for anybody but themself is a Christian in name only.
When we look at others, we don't see them and the things they do in totality. We can't see the full goodness or evil in another human or the mixture of both.
So many of the "faithful" see fit to appoint themselves as Man Almighty in stead of Man the servant of God.