Someone who is prone to violence or other forms of abuse should never get married.
Oddly enough, someone with a genetic illness might make a great spouse for someone that kids are not in the picture. As long as the partner knows the type of illness and what the long term (or CV the short term) outcome is, there is no reason for these people to be kept apart.
A few years of happiness is better that no years of happiness. (And it might, just might turn into many years of happiness, with medical magic being what it is today.)