The first thing that comes to my mind is that fact the mass rape could occur during war times. I'm thinking there's no way they thought these women enjoyed being undeniably raped and enjoyed it. Also, no one ever stopped to ask a women who has never had an orgasm how is it possible she has children. Did a women's thought really mean that little? It seems so obvious to me an untrained professional but what was the disconnect back then that prevent people from seeing this?
Not an answer but there is sort of a factual error in what you've written. Orgasms do not equate to "enjoying it". People can have an orgasm even if they are being violently raped. This is also a factor that causes a lot of psychological distress to victims leading to self blame and other issues because sometimes they themselves infer that this meant they enjoyed it.
This doesn't necessarily mean your question makes no sense, but it's worth baring in mind that just because a mass rape and pregnancy occurred it doesn't mean someone with the belief you state would necessarily have reason to question this.