And also a lot of things that "defy nature" are good, like polio vaccine.This seems more like something that people like to believe in because they want to feel special than something that is likely to be true. I'm not saying I believe in reploids, but with all the planets in the universe, how could life have arisen just once? Especially because we're finding more and more that life can survive in places that we thought it shouldn't have been able to. There are bacteria deep within the Earth's crust. Microorganisms that live off of sulfur or thrive in the extreme heat of undersea vents. Hell, there are even crabs that eat that stuff that lives in those undersea vents. These creatures never see the sun, but seem to be doing just fine.
If I need to appeal to your Fi... maybe Avatar is real?
Also... if we're talking about something being pure because it's nature, a lot of sex in the animal kingdom is nonconsensual. I don't think it's a good idea to look to "nature" for morality. That's the same path that leads us to PUA bullshit.