I had a brief encounter today with one of those braying jackasses who say that linguists are laissez-faire types who think that anything goes and no usage is ever wrong. You've encountered the type.
As evidence to the contrary I cite post at Language Log at which the distinguished linguist Geoffrey K. Pullum comments on The Wall Street Journal's having allowed the solecism childrens' into print more than a dozen times:
The rules for where you put apostrophes are strict and well-known spelling conventions. There is virtually no latitude in them. (You can perhaps spell things like P's and Q's as Ps and Qs if you really want, and some people still write Clive James' books rather than Clive James's books, as if the final s on the proper name James were the plural s, but that's just about all the flexibility there is.) There is no developing dialect split here; we are looking at slips of the pen.
Descriptive linguists base their claims on evidence about how English grammar works, not on dogma; but the 15 examples above do not form part of the evidence. They are better regarded as evidence that in at least 14 instances between 1987 and 1989 certain writers for a distinguished national newspaper made small spelling mistakes.
Not everything you read in the papers is true; not everything you read in the papers is grammatical; and in fact not everything you read in the papers is even data bearing on what's grammatical.