So if I understand this correctly, those who are not able to contribute good, solid genes to the next generation are not deemed fit to reproduce. You know what, let's say that you have someone with a family history of amyotrophic lateral sclerosis. This is a nasty neurodegenerative disease that can cause muscle control loss to the point of not being able to breathe without assistance, decreased cognitive function, and is fatal with no solid treatment to boot. It makes sense that they shouldn't have kids, right?
Oh wait, doesn't Steven Hawking have that?
Or what about those with mental retardation and bipolar disorder like you said? Take a person with both serious mental impairments and blindness to boot? Why don't you take a look at him play the piano? http://www.youtube.com/watch?v=U_GUPcg25QI
Or what about someone with bipolar disorder? Ask Georg Cantor, who got the Sylvester medal from the Royal Society, which is the highest mathematics honor they can bestow.
It is impossible to determine one's future based on what they are born with and what they can pass down. Each of these people that I have mentioned have made invaluable contributions to their respective fields, which never would have come about if their parents were unable to breed due to a couple of poor genes.