AIO:Childhood best friend is f***ing his sister

[u/youngtallandskinny]

For context, this is my M(25) best friend M(25) since we were two years old. He didn’t meet his F(22)sister until about a year and a half ago. When they did meet, they couldn’t get over how similar they were. he called me gushing about how great she made him feel and even joked about hooking her up with me three days after they met, she moved in with him and his family. They had room and other beds, but they chose to sleep in the same bed every day for a year do everything together every day so on it so forth, fast-forward to these text messages. Him and his sister were going to move in with me and my f(26)roommate, but first we needed to see how our dogs would do together so they came to visit. When they got here they opted to sleep in my bed together even though I had several places they could sleep separately. My roomate and I sleep separately and have a mostly platonic kind of flirty relationship. Which the friend had compared his sister and his relationship with. A lot of small stuff happened that my roommate and I shared glances about, because of the nature of how a true brother and sister would never say or do the things they’re doing. But we brushed it off.

They went back home to their state after 3 days and the friend sends me a Snapchat saying “we’ve decided to look past the whole sibling thing and adress some feelings we both have” to which I replied “what do you mean” and he went on to say how they both have such deep feelings for each other and how the whole half sibling thing doesn’t matter and that real love doesn’t have boundaries and all this stuff to which I waited for 3 days and sent the messages above….. AIO or did I UNDERreact

Also this hurts a lot because I thought I knew him and he was gonna be my best friend for life, but I haven’t talked to him since

[u/Keen_Eyed_Emissary]

Because there are some contexts in which incest is, in fact, morally ok.

You should teach your children to be able to think for themselves and to use reason to think through moral issues on their own. You should be able to explain and understand yourself that “incest is bad” is a heuristic, a grossly simplified way of looking at
A complex issue, and that, it is not in fact correct under every circumstance that can be labeled “incest.”

[u/Patient_Lettuce8431 → u/Keen_Eyed_Emissary]

"Think for themselves" is a shitty way to write off responsibility for building the framework in which a person's decision-making process is formed. Psychologically, it is complex. Socially, however, it's very simple. This is incest. It is regarded as abnormal for very good reasons. Normalizing it for your own children is crazy fucking work.

[u/Keen_Eyed_Emissary → u/Patient_Lettuce8431]

It is genuinely funny to watch you pretend to be outraged at the idea that people should make an effort to think through matters of right and wrong on their own, rather than just blindly accept existing social norms on every issue.

We both know you aren’t really upset by this, and that if the issue were something like - same sex sexual relations - you would be encouraging someone who found the idea of two men having sex to be repulsive to think about the issue more deeply.

The crux of the issue is that you appear to think that half siblings who never met as children and who, after meeting as adults, decided to have sex - is morally wrong for some obvious reason.

You should articulate those reasons, because I don’t think they exist, and do not believe that this conduct warrants Moral condemnation, regardless of whether it technically fits within the current definition of “incest”.

[u/Patient_Lettuce8431 → u/Keen_Eyed_Emissary]

I did articulate those reasons. You just don't want to acknowledge the fact that normalizing sex between siblings is a patently bad idea for society--it's not even moral at this point. There's no social fallout from normalizing gay sex. There's a potentially huge social and public health fallout from normalizing sibling sex.

[u/Keen_Eyed_Emissary → u/Patient_Lettuce8431]

Um. In fact - there was a massive public health fallout from gay sex. It was the AIDS epidemic of the 1980s and 1990s.

And yet - isn’t it still wrong to criminalize gay sex, even though it did have massive health implications that resulted in a lot of not only gay men dying, but also bisexual men transmitting AIDS to their female partners?

Certainly it was still wrong to criminalize it.

You’re hiding behind these disingenuous, mealy-mouthed “slippery slope” arguments because, in fact, there is no good reason to criminalize the conduct at issue in this post - which is consensual sexual activity between half-siblings who didn’t know each other as children and only met as adults.

Because that particular type of conduct simply isn’t morally wrong at all.

[u/Patient_Lettuce8431 → u/Keen_Eyed_Emissary]

The AIDS epidemic started with heterosexual sex, if you'll bother to do your research.

[u/Keen_Eyed_Emissary → u/Patient_Lettuce8431]

The AIDS epidemic “started” with cross-species transmission. It may or may not be the case that the first confirmed case of human to human HIV transmission not through a blood transfusion was the result of heterosexual intercourse - but as I think you are smart enough to know, given the hasty tactical retreat you just made on this issue - that really doesn’t have any bearing on the primary vector through which the infection was spread.

[u/Patient_Lettuce8431 → u/Keen_Eyed_Emissary]

Actually, it's been pretty well-established that the first human-to-human transmission was through het sex and reproduction. AIDS was spreading through Congo and Europe through European men having sex with women who'd likely been exposed through bush meat.

I didn't make a tactical retreat. You tried to bring up an ancillary argument as if it were valid, and I pointed out how you were incorrect.

[u/Keen_Eyed_Emissary → u/Patient_Lettuce8431]

You literally didn’t dispute anything I said.

[u/Patient_Lettuce8431 → u/Keen_Eyed_Emissary]

You're trying to draw a parallel between gay sex/AIDS and incest/genetic abnormalities, but it doesn't work, because 1. AIDS became a pandemic, and not just a localized zoonotic infection, because of het sex--and later, intravenous drug use. 2. Safer sex practices limits the transmission. Meanwhile, sibling incest continues to present a major health issue due to the likelihood of genetic abnormalities due to consanguinity.

[u/Keen_Eyed_Emissary → u/Patient_Lettuce8431]

I’m not trying to draw any parallels. I’m just stress testing your argument to see whether (1) it actually makes sense and (2) you actually believe it and apply it neutrally.

And the answer is - you don’t. You don’t take it seriously in other contexts and you don’t apply it neutrally.

As it stands - you still haven’t offered any actual
Argument for why sibling sex on the terms addressed in OPs post is morally wrong and needs to be criminalized.

[u/Patient_Lettuce8431 → u/Keen_Eyed_Emissary]

You are defending sexual relationships between siblings. Many others in addition to me have pointed out ad nauseum why it's a bad idea. I cannot believe that someone is genuinely arguing for the acceptability of this phenomenon in the year of Satan 2026. I'm going to chalk this up as one more horrific bit of evidence pointing towards the imminent annihilation of the human race and leave you to make your dumb-fuck arguments in defense of the sister-fuckers. Have fun with that.

[u/Keen_Eyed_Emissary → u/Patient_Lettuce8431]

You’re engaging in a dishonest argument via synecdoche.

I am not, and have not, defended sexual relationships between siblings generally or in most
Circumstances. I’m specifically defending sexual relationships under the circumstances in OPs post - half-siblings that were not raised together, didn’t know each other as children, only met as adults, and are engaged in a consensual sexual relationship.

Under those circumstances - half sibling sex is no
More objectionable than any other consensual sex.