We seem to know enough even if not the specifics. And I wasn't saying anything, just pointing out that purebloods are not the source of all evils as you like to pretend.
As Dora pointed out, we might be able to get back. Maybe we shouldn't even attempt it. Going back, as tempting as it is, could change everything. I know it sounds like a good thing, but things are never so simple. We might end up erasing people from existence.