At any rate as these cases are so rare and in most cases siblings of a chimeric person are normal and so is that person's offspring, there is no excuse to try to keep them from propagating.
I think you greatly underestimate environmental effects in placing so much importance on genetics. Many birth defects result from environmental causes such as illness of the mother (rubella), absence of necessary nutrients (spina bifida), or presence of foreign chemicals (thalidomide).