While I 100 % agree with the general sentiment that this is a terrible idea, I think your line of thought is a bit off. We have been made by evolution, a process built on the simple fact that any change that is too crappy will prevent itself from spreading, since the carriers of that change will be less likely to reproduce. Evolution is extremely efficient at preventing really crappy modifications from spreading. Thus, I don't think our primary concern should be about these modifications "entering the common gene pool". If they really are shitty modifications, their carriers will be less likely to survive/reproduce, and they'll be watered down/wiped out by evolution.
I think what we should be worried about is twofold: First, it's directly dystopic to imagine children born with defects that have been wilfully introduced, and which may not become apparent until in many years. Experimenting on unborn children this way is absolutely abhorrent. The second is the possibility that this actually works out in some ways, and is reserved for the super-rich, in which we can literally end up creating a human super-race that will inevitably suppress and exploit the rest of humanity.
Basically whether this works out or not, all outcomes look pretty bad. The only ethical way I could see this being done is using it to remove known defects such as hereditary diseases, and doing that through public programs aimed at eliminating those diseases at a population level. Doing something like that hinges on the program not being run by people like the one in the article.