Good science has pointed out that some illnesses are more likely for people with certain genes. And these illnesses (e.g. some cancers) cause lots of people lots of pain and can cost society in general a lot of money to look after the sick person.
So if we have the gene is it morally right to create an offspring who will possibly have to suffer the pain of disease and is it OK to possibly put a financial burden on society and exect it to pick up the bill?