A frequent criticism of things like life extensionism or human genetic
You got me! :-)
Only a strange kind of conservatism -- that things, that we, should never change -- would seem to support that view. Unless there really is something more to the view -- it's not the 'loss of humanity' per se that is 'bad' but the specific changes in question that would be bad ... e.g. extending life might make us all older but not healthier or better, might cause a massive drain on public resources, would promote quantity over quality of life, etc. ... re genetic modification, perhaps what's worrisome is the unpredictability of it all (once we tinker with genes who knows what mutant freaks we might create and what awful consequences might ensue) .... So I think an appropriate response to anyone making the claim you object to would be just that: just what precisely IS bad about the change i question .....
hope that's useful