‘Completely making a mockery of both grammar and common sense...’
The same thing happens every day right here in the US; read through ANY post-modern text and note the use of the inclusive ‘they’ and ‘them’ rather than the grammatically correct ‘he’ and ‘him.’
It’s easy to laugh at the idiocy of the Swedes, a bit more difficult to see the same thing happening here at home.
As for grammatic correctness, well yes strictly speaking it is incorrect, but who defines what is right anyway? The ultimate arbiter of what constitutes "correct" grammar is usage after all. And getting round this gender identification problem by the use of plurals is becoming increasingly common in everyday speech.