@E--JIROU Honestly I'd rather 0 incest. These "My parent got remarried and now I have a new sister/brother" are always romance for some reason! I've never seen a single one thats a good heartfelt "Lets learn to be siblings and have a happy family" I would love that.
Well partially because a fetish, why is it so popular? Because one of the siblings actually has hots for the other especially when they "meet" in ages like 14 and up(i.e. many real people experienced it or at least thought about it). I would never consider that person a sibling, a friend maybe or like a distant relative.
AND FOR CRYING IT OUT LOUD, it's not incest.
Incest (/ˈɪnsɛst/ IN-sest) is
sex between close relatives, for example a brother or sister or cousins. This typically includes sexual activity between people in consanguinity (blood relations), and sometimes those related by lineage.
It's like people learn buzzwords but not their meaning and definitions.
I for one think this kind of relationship is actually stronger. It's something akin to arranged marriages where parents of the married couple meet and actually get to know each other. In this case their parents are married and they are married thus both of them are keeping the others in check, so that the other party would be respectful. Also this brings the effort part a bit stronger, when your in-laws don't have any influence on you or your family you get our western world dating environment, where spouses disrespect each other and cheat more openly and without consequences.
Just as FYI, i don't have step-siblings but i don't mind non-blood related people to love each other.(Step parents and step children though is a kinda a taboo, it's literally "legal" grooming, which makes it far worse than many other alternatives)