This argument is based on speculation rather than fact. We have no proof that genetically modifying babies will prompt individuals to take advantage of the procedure, using it to increase their own social standing. By avoiding the procedure based on this possibility, we deprive couples who could benefit from it of children out of fear.
At second we right now have mental disorders like ADHD, BPD, Schizophrenia, Autism etc that destroyed ability of the kids to get good education and job. What is essentially the lack of equal access to resources provided by society.