Thanks @k-a-s-i-a for your insteresting post. If we consider ethics, modifying or selecting human DNA can be also an economic problem, where we will have "perfect" rich individuals and "not perfect" poor people. So changing nature can be good for giving as more chance of survival but also will have other consequences.
What is an allowed selection? color of hair or eyes? good memory? athletic disposition? what is allowed and what not?
On the other hand humans already play with DNA many centuries ago, breeding different species (plants and animals) through human guided selection. Also we as indivituals select sexual reproducing peers - these may be different, "natural" selections, but in the end in the fight for survival of a species as a whole, believe we might want playing all cards that we have. Fascinating subject.
RE: Where should DNA modifications stop?