how u doubt sasuke banged karin? karin is the mother of his child, and they call him bastard because he didn't tell sarada the truth, that and probably the fact that he hadn't seen her for so long he forgot how she even looked like.
probably because Sasuke never told Salad that Karin was the mother. There was something about the way he's been looking at her, almost as if he never wanted her to know.