Are "designer babies" ok?

This week, Britain voted to be the first country to allow the "three parent" in vitro fertilisation. It is a treatment that doctors believe will prevent some inherited, incurable diseases but which critics view as a step towards creating designer babies. These babies will be born from genetically modified embryos with DNA from a mother, a father, and a female donor.
 
It was initially designed to help families with mitochondrial diseases passed down the maternal line such as fatal heart problems, liver failure, brain disorders, blindness and muscular dystrophy.  
 
As much as this is great for medicine, the critics believe that some parents would abuse the technology to modify their children for their narcissistic needs. For example, create children with what people think is more attractive traits such height, eye colour and hair texture.
 
I see this technology as a great thing. Many mothers who know that their family has a history of mitochondrial disease fear conceiving because of the chance that the disease might be passed to their children. I hardly believe many parents would use this to create the so called designer baby.
 
What do you think of this technology? Do you think this treatment is good or bad?