How about this: Yes, linguistics is descriptive. In the world we live in, some people say "aks". And that is regarded as a marker of lower class/uneducated people, and is not generally used by educated/upper class/professional people.

It seems to me that linguistics should note that, yes, it is used, and it has a very definite meaning, and it has a connotation about the social class and education of the speaker, and is therefore considered socially improper even if it is linguistically proper.