I was going to use the comparison "Humans born mentally handicapped to the point that their cognitive function is equivalent to chimps." (This avoids the potential issue of "babies grow up to be average humans.")

Along similar lines I was going to propose that it should be considered moral to test on "Low IQ Jocks as soon as they finish High School". After all they have finished their glory years and are different to me in similar ways to how I am different to a chimpanzee. But I decided not to post because I decided it was dangerous to go anywhere near a space including "different" and "less moral consideration".