If someone has a genetic disease/illness, should they do everything they can to prevent from passing it on?

A few hereditary diseases are as follows: Down Syndrome, Thalassemia, Cystic Fibrosis, Tay-Sachs disease, Sickle Cell Anemia, Huntington disease, Marfan Syndrome.
If someone has a genetic disease/illness, should they do everything they can to prevent from passing it on?
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