That's based but to be clear the birthrate issue isn't only a sexual issue.
In order to have children a man has to have trust in the future. He must at the very least be reassured that what he invest his time, money and energy in will effectively remain his property : and yes, I'm talking about women.
Mass rape isn't possible for reason I've explained before : either women are protected by the law and you can't rape them, or they trade sex for protection with strong men and you still can't rape them, because said men won't let you use their property.
What we need is a system of incentives to push people to create and maintain stable monogamous structures, that mean :
- ban contraception
- ban abortion
- make sex outside marriage illegal
- ban women's rights
- ban women from universities
- ban women from 80 % of the job market
- ban divorce
- ban child support
- brutally repress all media, influenceurs, celebrities promoting anything remotely feminist
They will have no choice but to get married, make children and take care of them while being submissive to their husbands.
And that will boost the fertility rates.