The whole point of the common core, from my understanding was to be vague enough to let local governments decide how best to implement it. They were trying to avoid "one size fits all."

Having everyone in the same page with regards to an overall standard seems good in my book.

Mathematics is one of those few areas where there is only one right answer to most problems. You can have different methods of arriving at that answer, but in many cases one method is optimal and can be proven as such.

Mathematics isn't cultural. Numbers and the laws that govern them aren't going to change in response to how people feel about them or who is teaching them. I fail to see the benefit of working without objective criteria in this domain.

This standard isn't one size, its a system of measuring sizes. The size or sizes chosen to fit the particular purpose is an implementation detail. Your argument is like calling all shoe sizes "one size" because there is a standardized, limited range of choices.

"One size fits all" is the only possible answer when you have multiple, mutually contradictory goals.

The idea that even just one child out of millions might be left out means no answer that treats the problem on an individual, child-by-child basis can ever be considered.

It also rules out anything where one child might get "more" than another. (Never mind that many people are perfectly happy and comfortable despite having gotten less than others.)