I get the feeling that this is was the attitude take by the people who did all those bad things in the first place. Maybe they would have explained it as 'what god gave them'.

But that's neither here nor there - it's either your system now, to try and make things more equitable for the next people to come along, or you are part of what's keeping the unjust system in place.

So, sure, there's no reason to feel guilty for whatever anyone did, whenever they did it, and however much DNA you share with them. But, what >you< do to fix it, well, that is your responsibility, and your guilt if you do not.