Variation exists that is non-pathological. There are lots of different ways to code a muscle fiber, for example. There are also lots of ways to code half-functional, disease causing muscle fiber. Believe me when I say I understand how genetics works. I don't pretend that selective breeding is a cure-all, and if it were misapplied, we would lose a lot of beneficial genetic diversity. I'm not against genetic diversity, I think it's important. But the spectrum is wider than just 'good' genes and 'bad' genes, as you stated. We know more now than our ancestors. That obliges us to use that knowledge for the betterment of the species. That obliges us to use that knowledge to reduce suffering where we can.Well it's not like you can have one without the other.