All of those other taboos actually happen on the regular and without anyone being shocked. Incest is super common. Lolicon themes are, too. And cannibalism, well, we all just saw Slime. It's only rape that causes an outrage, which I find endlessly hypocritical.
Also regarding torture: I'd agree that at some point torture becomes worse than death. See the shit that was done to the heroes of Ajin and Tokyo Ghoul. But 'forced sex' definitely is far from that.