It wasn't rape but rather a brutish way of having sex however again it was to show the character progression of Drogo from Primitive Man to loving husband and Danny's ability to use love and forgiveness to change people.
None of this is simply thrown in to tititalte. It's all there for a reason. GOTs is very much a morality driven story with a messsage. However without the darkness you can't see the light.
It's softcore porn for hobbits.
