Unfortunately, you are flat wrong.
In modern societies, less-successful members of society invariably have a MUCH higher birth rate than more successful members.
The abortion/infanticide of the truly retarded may indeed reduce their numbers as a percentage of the total, but then they’re not really the problem, as they’ve always been a small percentage. The left end of the bell curve.
The problems at present is the “dull normal,” say 80 to 90 on the IQ scale, of whom there are about the same number as the “bright normal,” or 110 to 120. There are a large number of these people. And they’re mostly those who are reproducing. IOW, they are “the fittest” in Darwinian terms despite not being fit at all in an economic sense.
There is little demand (in the economic sense of the term) for the dull normal in our economy, and the IQ level for which there is no demand continues to creep upwards yearly.
I don't disagree with that, and that doesn't contradict what I've posted here. My point is that the decline in birthrate for one group as a percentage of its prior birthrate is actually higher than it is for the other group.
Look at black Americans, for example. They represent something like 12% of the U.S. population but account for more than a third of all documented abortions. At 35 million abortions since 1973, we've basically eradicated 10-15 million black people who now don't show up in any of our statistical analyses of IQ, living standards, criminal records, etc.
What do you think the collective IQ of the U.S. would be if all of these people were alive today? I don't know the answer, but I suspect my previous post is applicable to this.