I'll try to clarify although I'm surprised ad hominem attacks constitute debate on philosophy threads. I guess that is par for the course on Internet forums of all types.
1. Humans have no concept of how to make a superior being. We value intelligence, so your idea is to make smarter humans. If apes were in the same boat, they would possibly choose to make stronger and faster apes since that may be what they value. I doubt anyone would try to make the humans that Greg Bear envisioned in Darwin's Radio
but he made a good point: humans may be dramatically improved by focusing on something other than intelligence.
2. (or maybe 1a) By emphasizing certain aspects of the genome, you will certainly deemphasize others. How can you chose what is unimportant? By making the best possible human, you tend to block out traits that could be important to humans making the next evolutionary step. You could be engineering the very best horse buggy ever made when you should be working on how to make cars.
3. Genetic uniformity results in dramatically increased susecptibility to disease. We see this in farm crops and domesticed breeds of animals. There is an ant breed that farms fungus and even there, the cultivated fungus has become much more susceptible to disease. By breeding out the genetic diversity from humans, you make humans more at risk of being wiped out by a new super disease.