And what is wrong with a little sadism once you understand it. Masochists need sadists in order to fit in and function in society. We don't go around kidnapping people off the streets, we use those who wish to have pain inflicted on them.
As for the topic of incest, look at the flood of porn sites that use the phrase "step-" as a way to skirt around the legal issues. And the amount of erotica written by women about seducing their step-daddies. Also, there are several states here in America and countries in Europe where incest between people above the age of consent is legal since there are no laws against it.
What does "underaged" mean today? Look at some of the porn actresses like Coco Lovelock who is 24 but looks like she is 14-15 in her movies. In Japan, they get small, young women to convincingly play the part of young, underaged girls in their videos. And don't use the argument to look at their genitals, because women from Eastern Europe have genitals that look like underaged girls, just check them out. In the age of 18 USC 2257 rules, no one blatantly shows underaged people on their websites and just because they use certain words, they shouldn't be banned.
Hell, given the choice between between zoophilia and underaged porn, most normies would prefer to see zoophilia banned over underaged stuff. I have heard this opinion voiced more that a few times during discussions at parties. That is why we all go to some lengths to keep our desires hidden.