If procreation makes someone happy, there is nothing we can do to hold back the scenario of someone passing on bad genetic mutations to the next generation. We've all met people that we say to ourselves, "This person has no business having biological children." Yet, we live in a free society where everyone has the right to their own beliefs even if that belief includes faulty thinking in the gene pool.
As someone who has a fifty-percent chance of passing on a serious genetic mutation, I decided not to have biological children. However, in most cases, this should remain a person's choice. If we get too far into limiting people's choices, then we will become like Hitler in his belief of one pure race. People really need to be able to think for themselves and make choices that are in the best interests of their potential children, though.
While it shouldn't always be encouraged, it is not the place of someone to tell someone else they can't have children. People have a right to make the decision for themselves and the bodies and reproductive organs of people belong to them alone. Banning reproduction for one thing could lead to bigots attempting to ban it for things like race or other reasons that are bigoted.
Whether someone has a disorder or not they should still be allowed the right to children. Just because they have a genetic disorder does not mean that their kids automatically will and it does not mean that child would not enjoy life. They deserve just as much a chance as we do.
If a significant genetic mutation that causes a serious condition or illness is going to most likely pass that on to a child when he or she procreates, then there should be some way to prohibit that procreation so another child doesn't suffer. There are children who can be adopted and loved without taking this risk.