But no one is talking about actual incest, they are talking about a cheap storyline in a stupid online video made by consenting adults pretending (and actually) not related by blood.
If you have a moral objection to the content of the video, don't watch it, if you don't want to let people consume media that has objectionable themes, let's ban all violence as well, not just in porn, but movies, music, literature. No more Jason Statham, no more Daniel Craig, no more Dwayne 'the Rock' Johnson, no more Marky Mark, no more Eminem, no more Homer (sex and violence), no more The Bible (sex, incest, violence, rape, genocide, polygamy, slavery, child sacrifice).
"Step-cest" - a term I am sure has existed before, but I'm claiming it now, is make believe. And I'd bet 90+% of the watchers have it on mute.