why grant amnesty?

I know what the southerners did to these slaves was unbelievable, disgusting, disturbing. Yet Lincoln forgave them for all of this. I believe this was ridiculous, for someone to treat human beings to this extend have no forgiveness. Not even in the eyes on God. They had control over most crops and farming land, and made these african americans work for these lands. If I was Lincoln, I"m sorry but I would not grant amnesty, not at all.