Let me answer, at the cost of perhaps making myself look foolish.
You couldn't possibly look foolish for having such feelings, in my opinion. Angst over academic performance and IQ must be worse than normal for parents who have one child who significantly underperforms another. Maybe that's how it will be for me-- my second son had a significant expressive language delay and is developing quite differently from my first.
I usually think of these issues as arising due to parent competitiveness with other parents, or from wanting one's children to have opportunities or successful outcomes. In the linked story, though, I found the opening particularly poignant ("I want my daughter... to think she’s one of the smart kids") even if it is partly motivated by performance concerns. Everyone wants their children to have a positive self-concept.
ETA: ... but I also agree with MegMeg.
