The difference is that now you're talking about social constructs, not the natural world. We cannot force the real world into accordance with our notions of morality the way we can with society. In terms of the physical world, reality exists, and it is what it is, regardless of how you or I feel about it - society and culture are bit more flexible than that. We can make them or unmake them as we see fit, but we are entirely powerless to remake the natural world in such a manner. I don't care for gravity much, but it's not going away just because I don't like it, so I might as well learn to live with it.
And so it is with evolution. It's sad, but true - the facts on the ground will mug your beautiful theory every time, and there's nothing you can do about it.
Interesting.