Why an allegory?
I've just seen this movie for the first time...
Wow...
Beautiful, dark, bizarre and haunting.
But when I read the posts of the main metaphor of the movie (symbolic marriage breakup) I couldn't help but think - why not take it seriously?
The movie is ambiguous, yes - but why can't the possesions, monsters and murders be real?
Why can't it be about a demon (the Antichrist, if You will) being born and nurtured to bring an end to humanity?
Most of the movies alegories are about god (or his absence) then of the metaphorical marriage. Maybe the "only good in the world is mirrored from darkness" - maybe the only god is the devil?
Personal tragedy is good - but a doomsday scenario is better (if Your looking for a horror movie).