It leads to K-shaped education where parents who recognize the deficiency of public education simply teach their kids math themselves or hire private tutors. Public education used to be a force for equality of knowledge in the country. Now it perversely does the opposite, all in the name of education!
Except that's not what the data shows. The decrease is similar across performance levels.
At least in elementary school I don't see the deficiency in common core math compared to what I had 30 years ago. My kid has been exposed to a wide variety of topics sooner than I was, and she's way stronger in word problems on top of that. Do people have a specific complaint with elementary school common core math that we should be teaching but aren't, or vice versa? Or is it more problematic later?