If you start going down this path, you'll end up at a nasty place. Who gets to define which genes are bad and which are good? If we find a gene which will pre-disposition people to be a little more violent, do we add that to the list of "bad" genes?
Don't get me wrong, there are bad genes out there - ones which increase the likelihood of being afflicted with breast cancer, for example. There are genes which are just plain broken - they don't produce the protein they should and the person with that gene suffers from it. Huntington's disease is genetic, and that's a nasty, nasty disease.
But if you start saying "You can reproduce and you can't", that's when all the trouble starts. Who makes the decision? How do they enforce it? In my opinion, what little good you'll get from banning people from having children will be outweighed by the abuse and sheer misery that will come along with this sort of system.
Now, I'm all in favour of curing genetic diseases. But instead of going down the negative path of suppression, why don't we instead embrace the positive path of gene therapy or corrective medicine? Instead of banning people from having kids, why not find ways to fix or replace the genes? You could give people the voluntary option of eliminating the bad genes while not eroding anyone's rights.
I can sympathize with what the Eugenics crowd wanted. But there's a BETTER way of going about it than banning people from having kids. Let's cure the person (if they want to be cured, they have a right to refuse medication), instead of taking away their rights to have kids. Let's fix, instead of break. Let's find a solution that will make everyone happy. With science.