Earlier quoted context omitted.
You're treating that theoretical average or median, even if no one speaks that way, as the standard accent against which all others are compared. That's one way in which people sometimes choose a "right" or "zero" accent. Another is by social standing ("the queen's English" was literally that). Either way, that's declaring one accent the right way of speaking, and describing people who speak differently as having a "…
It declares it standard, not "right". If you learn a foreign language having a standard to aim for is good and large deviations are difficult. Stop trying to turn this into right or wrong.
In linguistics, this is the prescriptive vs descriptive debate. It's not controversial that a prescriptive grammar declares how a language should or ought to be used. Declaring one accent the standard is a similar prescriptive position.