@vikorr,
It only affects future generations if people are living to reproduce who otherwise would not.
Breast cancer generally has never killed people before reproductive age...heart disease...except for the kind of genetic anomalies that used to kill people as kids or young adults, ditto.
I suspect allergies and asthma are more linked to over-protection of young babies from germs, and the plethora of new things to be allergic TO.
Again, allergies, except extremely severe ones, generally didn't kill.
I mean, given that the death rate for babies and children used to be so high, I guess we used to have to be fitter to survive...but a lot of these deaths were from infections, not genetic illnesses.
I think there IS a real decision to be made when you know you have the potential to pass on real genetic problems.
Eg, I have a 2 in 3 chance of being a carrier of cystic fibrosis. (My sister died of it, and it's obviously a recessive)
The man I was most likely to reproduce with also had a sibling who died of it.
He therefore had the same odds as I.
At the time, there was no genetic test and no test for a foetus.
We decided not to take such a risk....it being a horrible fatal disease (though sufferers are now living MUCH longer.)
