
Though let me be clear, I'm not advocating for bestiality, incest, or anything, but if someone does it and it's as consensual as possible, I don't see why I should oppose it. You can find videos on Youtube where dogs hump people (completely sfw), it's often brushed off/laughed at because most people aren't into it, so they are more likely to find it either funny or weird.
Regarding rape, to be honest I've seen (on internet) quite a bit of women/men that are into fantasy of it - and fantasy is possible to control. Some even play it out with the help of their spouses, with help of safe words, I'd guess, but I'd bet that most if saw something like that happening in real life to someone, they'd do their utmost to stop it. I know I've played some adult games that border on that, and in the fantasy and context I'm okay with it to a point, but in real life I'm repulsed by it completely.
There's plethora of fetishes people are into, to some other such as cheating - I've recently saw a board where women and men bragged openly how they screwed other men/women outside or marriage, and some of them had children by other men (assuming it's true, because internet), and even other fetishes such as hotwifing/cuckolding where both partners are into it, or even further where women enjoy and encourage their husbands to engage with other women, to bring them home/screw them/etc, which they find enjoyable for various reasons.
But most of such things are a bit 'out there', and most of it seems to be just a fantasy. People are sexual beings and at the same time into the most vanilla, and weirdest things, and fantasy - whether it's games/porn/stories helps sate their desires.
With your last point @Mortze, I absolutely agree, I don't think anyone should be forced into it, or for that matter abused, and everything should be done to make sure it doesn't happen. There are various articles (as well those opposing it) as to why pornography is good, even for relationship, especially if both partners watch it.
Regarding some of the fetishes above, it's estimated that 1-3% of children are concieved outside of marriage/relationship, and that's only those that either didn't take adequate protection, or didn't care enough if they get pregnant or not - so the cheating percentage is probably higher, for men too. However, I think a) fantasies about it, especially so many in porn, etc and b) communities, might help and reduce that, in a way, that's my theory only, though, because they might see there are others, and find willing partners who are into it. I'm not sure how accurate that is, but I think future will show.
As for games, one of the more famous (though it's more interactive fiction) that I know of is Fenoxo, who seems to be quite popular - around 5000 patreons currently, which comes down to 26.000$ a month lol. But I think with that, and incest as well - though he doesn't deal with incest as far I've seen, but mostly monsterish type of characters, imps, demons, futas, etc, the writing is quite important. The better writing is, more people will be interested. That's in part why I like Shark's games, because the writing and interactions are good, so even when it goes into things I don't normally enjoy, I still play them and try to find things I do enjoy.
My last point on the previous post is a bit out there, but one I've seen mirrored before, and while obviously animals can't really compare to humans, I think we also forget that we are animals too. There are animals that do - and try - to cross-breed, and even on Youtube you can find dogs trying to hump cats lol. Or for that matter, cats humping dogs which is mildly hilarious.
But it all comes down to: if no one is harmed, what is the issue?