My major concern about leaving enhancement to the marketplace is that then the rich will be able to buy themselves genetically superior children and the poor will not - sharpening the class divisions we have now. That problem could be overcome if, genetic enhancement were available to all, subsidized by the state - and that would, over time, have benefits for society as well.
Peter Singer...the nervous systems of other animals were not artificially constructed - as a robot might be artificially constructed - to mimic the pain behavior of humans. A capacity to feel pain obviously enhances a species' prospects of survival...it is surely unreasonable to suppose that nervous systems that are virtually identical physiologically, have a common origin and a common evolutionary function, and result in similar forms of behavior in similar circumstances should actually operate in an entirely different manner on the level of subjective feelings.
Peter Singer