Hmm... fascinating. Perhaps my respose was just me trying to get philosphical and failing
But in response, I don't think it's an actual "dualism" as in Eru has an evil equal or anything, but it seems that in his outline of the Song he has a plan for everything and knows what is going to happen, unlike any of the Valar or Morgoth. He's definitely a good force, but he seems to understand that good and evil both have their place.
Hopefully this clears some stuff up...