I think you're missing the point GC was trying to make, which is that the kind of child-rearing patterns that make "positive" geniuses might also make negative

I think you're missing the point GC was trying to make, which is that the kind of child-rearing patterns that make "positive" geniuses might also make negative ones. i.e. "all positive geniuses were given X, but not all people given X became positive geniuses (some became mass murderers).