I think your definition of descriptivism is incorrect. Descriptivism certainly doesn't mean everything anyone ever says is gramatically correct. Please read http://itre.cis.upenn.edu/~myl/languagelog/archives/001843.h... .
Coming back to the original point (and not in response to you in particular), using "begging the question" to mean "raising the question" is very common now, and trying to object to that does no one any favours.