I look at this from a different side. I have a genetic condition that is a heritable one. Any children I have will have a 50% chance of having it, and some studies say a higher percentage.
My parents had no idea they were passing anything on. It's likely one side of my family has it at a low-level, and I got it full force.
There is a spectrum with the condition, and I have it quite badly.
I have chosen not to have children. In many cases where people have had children - I've noticed they are usually (not always of course) at the lower end of the spectrum, so their symptoms aren't quite as severe. However - the level you have it, won't always be the level your child has it. They could be the same, better, or worse. You just don't know.
The one main thing that has made this decision for me is the pain this condition brings. For me it's constant, all consuming and in every part of the body. That to me, personally, makes it differerent from many other non-painful conditions as it's about quality of life.
I've wanted children for as long as I can remember. I can't imagine having a child and them asking me why I chose for them to have constant pain. I would feel awful, and would feel like I condemned them to a life like mine.
They haven't found the gene yet, so I couldn't test the embryo unlike this couple who were lucky enough to have a choice. I find it strange they chose to go ahead when there is an option to avoid - one many people with genetic conditions would love to have.