From this blog post quoting an interview between a German magazine and a Harvard researcher looking to re-create Neanderthals, we read this argument from the egghead: "The one thing that is bad for society is low diversity."
What is a society? This dictionary says it's raison d'etre is uniformity; we form and preserve society to protect and promote some common trait. Dr. Church says we must undermine our common traits to have a healthy society. I say this kills society itself.