i also feel a part of the wide-spread view is partially due to it not being too common, so there's little discussion of it aside from a black and white view of "family is family" or something.
possibly paired with the porn industry capitalizing on it, making it seem 'weird' or 'morally wrong', as porn is not considered okay publicly(i'm not sure how to word this, so i hope you understand what i mean) so seeing something that's widely seen as a 'kink' or 'fetish' so to speak and not as two people in a relationship may be the reason people are inherently repulsed.
i think one sign of this is that the biggest amount of discussion that's been centered on this is the memes(no but fr lmfao). iykyk
this is all just me guessing, though, and with the points I'm attempting to make, there's further prejudice behind those as well that lead me to this possible stigma.
What you need to understand is, these two will NEVER think of each other as siblings. They're WAY TOO OLD for that, and they've already had sex. An adult who's already working and supporting themselves is completely different from a minor still living with their parents, or even from a college student still needing their parents to pay their college fees and support them financially. Kids living with their parents and college students financially dependent on their parents are stuck accepting their parent's choice whenever one of them decides to remarry, so they usually have no choice but to get to know the new "step dad/mom and their kids" and try to get along with them as much as possible. But when you're already a working adult paying their own taxes, you think of both you and your parents as separate people who love each other but still want to carry their own separate lives. So, if your widowed or divorced parent suddenly comes to you and says, I'm marrying X, and X has a son/daughter, you don't instantly think of X as family. To you, they're just the son/daughter of your parent's new lover, and that's it. Chances are, you're not even going to live with your new step parent and sibling under the same roof, either because you no longer live with either of your parents, or because you already make enough money in your job to be able to move out and spare yourself the need to get used to living with total strangers who suddenly became step relatives (not because you dislike them, but because you're TOO OLD for that).
In this case, the mc discovered the guy he had sex with is the son of the same man his mother was dating and now wants to marry. Both the mc and his mother were each carrying out their own love-lives separate from each other and dating people without asking permission nor even introducing their partners to each other, so that is how this happened. Even before knowing the new stepdad's son was his ex lover, the mc was already planning to move out of his mother's house. Why? Because he's already a working adult who earns enough to live on his own, old enough to live alone and date without consulting his mother, and too old to be imposed the obligation of living with the strannger who's now going to get married with his mother. As an adult, the mc's merely asked to be polite to his mom's new guy, but he's not required to live with him nor call him father, let alone treat the man's son as a brother. The guy will be his step dad, but the guy's adult son will not be a brother, and will just be "his stepfather's son", no amount of marriages between their relatives is gonna suddenly turn them into siblings now. If on top of that, you add the fact that the son is someone he dated and slept with, then no amount of time as "step siblings" on paper is ever gonna erase that past. They *had* sex in the past, and people who've had sex will never see each other as family, even if a thousand relatives of theirs were to get married now.
Oh, I just saw your comments in another thread and think I may have misunderstood your comment in the opposite direction. If that's the case, I realize perhaps this didn't need to be explained, so sorry, you're free to ignore my previous post...(￣∇￣")
yeah, no, i think the one you're referring to i did state they aren't and won't think of each other as brothers.. lol
see a lot of people asking why anyone could be upset or w.e that they'll become stepbrothers now --and (most likely) continue their sexual relationship in the future
imo, the reason is pretty obviously because they're family. maybe only in name, but it's still considered 'morally unacceptable' by society's standards. depending on where you live, it could also potentially be illegal, but I'm unsure of it, it was kinda confusing when it came to some countries or states.
while it is legal in many places worldwide, realistically speaking, the main issues are just the views of the step-siblings' parents, peers, and general public/people who are aware of the fact. with that, if the parents have the same view of it being considered as wrong in some form of way, could cause discourse in the family and damage relationships, and it's something the couple would be forced to think about beforehand or if found out(if they're hiding it).
i'm not saying I personally find it wrong-- i'm honestly not sure how i'd feel about it as I've never been in that type of situation, but I am curious about if anyone has other reasons for why they don't like it/are uncomfortable with it.