Because it was never wrong in the nature

It's nature. There wasn't even the word or the idea of "rape"

It's simply survival for the species to pass down the gene and multiply so that human don't go extinct.

The Africans are projecting exactly what the nature is

It's only modern human forbid this because we have awareness how the opposite person feels like when you go against her will and force her to satisfy yourself.

It creates moral value and thus, we forbid it to prevent victims suffer. To maintain peace. To keep the community safe and protect the weak