Germ-line Engineering is the process that creates genetically modified humans a.k.a. designer babies. This technology is based around how bacteria defend themselves against viruses. When the bacteria is attacked, it sends guide RNA. The guide RNA, goes to the virus and, using enzyme CAS9, cuts out parts of the DNA, and replaces them. Scientists created CRISPR which is based off of bacterial defense mechanism.
CRISPR allows a scientist to screw around with an egg or a sperm's DNA. A scientist can remove a mutated part and replace it with a healthier part. They can also change the eye colour, change hair colour, skin colour, mental power, physical strength, etc. This all sounds great, but it is unpredictable. In an MIT study, only 20% of monkeys that had Germ-line Engineering, had the modified genes at birth (or any other time). So it only works in 20% of cases. In the 80% of failures, unfortunate mutations might arise. Also, some trials resulted with the death of the patient. So, it is not a good investment.
An issue with genetically modified humans, is the lack of genetical diversity. If everyone is changing their genes to create some desired qualities, then it is safe to assume the genetical diversity will slowly go away. Imagine a world were almost everyone is the same. Now imagine a world with genetically modified humans. You should be imagining the same thing. Now imagine if a superbug would arise. It would be the Irish Potato Famine, but with humans.
Many people complain about the rich having more opportunities then the poor. Well this would make the advantages a lot bigger. A "designer baby" is expensive. So only the rich could afford to create a prefect child. Now that sounds unfair.
Also, playing god is never a good thing. God made us in his image. Why mess it up?
(If you don't believe in God) We evolved into a powerful race. Why should we mess it up?
Evolution WILL create the stronger and superior race we desire. While we are tampering with genes we might screw up, big time. There are hundreds of horrors that could result from screwing with our genes.
We should stop researching into designer babies. NOW!