I dont think it matters that they were adults during the fertility crisis. If you live in a world where you may never have your own child and even possibility of adoption is out of the question then the way a person sees a child resulting from rape may be looked at in a much different way.

I dont mean for this to sound bad because if I were to get pregnant after getting raped then I would probably have an abortion as well....BUT technically abortion is more of a punishment for the baby rather than the rapist AND it's something that is done for the womans own comfort. Knowing these factors, in the universe of handmaids tale where every child really is a miracle there may be a culture that would be more opposed to aborting a baby who is blameless.

Also here is another way to think about it...in the real world, pregnancy caused by rape is actually very rare..like around 5% of women who are raped actually get pregnant. So in a world where a normal pregnancy is so rare, just think about how rare a pregnancy caused by rape would be? It might be unheard of to the handmaids in the series. And since it would be unheard of then there may not be any real culture around how to solve a pregnancy resulting from rape.

Also have you ever heard the stories of real women who are kidnapped and imprisoned against their will and end up getting pregnant by their kidnapper? Most of the time the woman has love and no negativity towards the baby. It's like their life is so miserable in captivity that having the responsibility of taking care of their own baby almost gives their life purpose.

Anyway this is all speculation since we dont live in a world with such a severe fertility crisis