Recessive diseases will probably be eradicated eventually, but the dominant ones need only an unaffected single carrier.
I can't really give a list of 'major diseases' barring
Category:Genetic disorders - Wikipedia, the free encyclopedia or something. I can give examples of what I think should be frowned upon:
*Diseases which are fatal and reduce one's life expectancy drastically (e.g. Cystic Fibrosis, Huntington's etc.) are the ones I'm most against, imagine your child knowing the age that they would die- around their thirties too-it would be fucking heartbreaking.
*Diseases which disable significantly (I can't really judge what's significant or not, but serious cases of Marfan Syndrome and Spinal Muscular Dystrophy are some examples) disallowing one from having the choice to live a healthy, average life. they don't have to be fatal but they might as well be
Other gene defects can cause seizures, or blindness, or two nubs to appear on the bottom of your elbow; most hereditary diseases are not deadly and do not reduce one's quality of life, there's no need to abort, no need to attach a stigma, these individuals are capable of fulfilled, joyful existences. Breed away~!!
EDIT: read katietully's post(s), I agree, who are we to say that the individual's life was in vain? but then again, what if it was? what if it was torture for them to go on?
who becomes responsible for the pain they've suffered? surely it's their parents? I see no one else that could be at fault