The moral and ethical issues that come with this concept of genetically modified babies lie strongly along religious beliefs. If you believe in God, and that He is in charge of our lives, and with giving us our particular traits, physical bodies and personalities, then science stepping in and altering the genetics can be deemed "playing God." If you don't believe in God, then such issues are not as big of a concern. Also, if you do believe in God, but feel that He approves of science for the bettering of humanity, then those issues won't play as large of a role either.
Using the modifications to eradicate disease also might soften some of the protests against such modifications. If you know that your child would be born with MS, for example, then it is very compelling to be able to alter them in order to enhance their quality of living. Opponents to that philosophy would again cite the playing God argument, or, on a non-religious front, might indicate that our genetics--for good or bad--are a crucial part of our human experience here on earth. Take away our weaknesses, and we won't turn out to be the same people. Weaknesses often lead us to become more strong, to have individual characters, and to learn to triumph over adversity, giving us a sense of self-dignity and accomplishment. That is more of an ethical argument that might be used.
Those are just a few thoughts to get you started; good luck!