In theory...

[Sensei Kiisu]

if we were to prevent all people with genetic/incurable diseases (such as down syndrome, cystic fibrosis, A.I.D.S, strong family histories of cancer/depression/autism) from reproducing, when everyone died out, based on Darwin's theory, we'd eventually have a super fit race of humans free from genetic diseases, and uncurable ones (since new people born could not inherit them)... this doesn't include common viruses as the cold, flu, or ones that aren't hereditary/incurable.

OR, can people who have no family history of any of these simply get them from abnormalities while developing in the womb anyway?

I'm not saying we should do this, and I'm certainly not proposing it or in favour of the idea - I'm just wondering would this theory work if it were to happen.

[Mythos]

Eventually due to the nature of DNA copying and the errors which inevitably mount up during the process, heretable diseases will appear again.

[Elfdude]

There's several mutations that are genetic but also caused by single point mutations or gene replications or etc. in the natural process of reproduction. Our genetic code evolves on its own. However there are several disorders that we could probably eliminate through eugenics.

The issue is that eugenics are tied to nazis which has poisoned the well for anyone trying to perpetuate the concept.