I mean, I do think incest is, ethically speaking, more complex than people often make it out to be. It's not necessarily wrong since, as you point out, it can be consensual, and arguing that it's wrong because of the higher chance of genetic defects reeks of eugenics, and also ignores that relationships are meaningful beyond their ability to reproduce (unless you're a christian conservative and just hate gays I suppose).
That all said, incest is universally frowned upon nowadays in most civilized countries, and if you ask any random stranger on the street they will likely respond with disgust. Which is why it's weird to find this lady just completely cool with the fact that her boss is crushing on her own son.
It's also very important to note that, though potentially fine in theory, incest is almost always accompanied by abuse and is very rarely truly consensual. If I found out two adults that I knew were related were in a happy relationship, I'd be shocked, but wouldn't care much beyond that. However, I'd be extremely concerned to find out this adult woman I knew was in love with her underage son. The power dynamics are simply too skewed for there to be a healthy relationship there, and I'd feel the need to intervene and look for signs of abuse and/or grooming.
Incest in fiction can conveniently ignore these problems by simply not making the relationship abusive, but any outsider to it would normally suspect something, because that's just the way incest usually happens. Convincing outsiders is also usually the final boss in those types of stories. I recall one about a brother and sister getting it on and them having to come out to their parents, which from what I remember ended in violence. So yeah, I'm definitely shocked this lady is so chill about it.
Like i said, the reason why Incest is frowned up, is because of religious & societal notions, which had been hammered into peoples minds for decades and centuries.
As for
"incest is almost always accompanied by abuse and is very rarely truly consensual", that's mostly a misconception or more like focused on excessively to portray Incest relation as a negative.
I mean, abuse and non-consensual issues are present in every situation, so why just pin it on just Incest?
I am sure, there are far higher number of Incest relationship which are consensual and total ok, but they aren't talked about, as if the info gets leaked, media would find some way to portray it in a negative.
As there have been cases where while the Incest relationship had been consensual, the media in someway or another turned it into being non-consensual or something bizarre, because that's what the current religious and societal outlook demands.
It's same as like 200 years ago, a Women showing a bit of skin was considered as immoral and heavily criticized, and some even relating Women exposing skin to being a Whore.
But now, Women go around half or even full naked (depending on areas) easily. I mean, no one questions if a Woman wears a bikini in a swimming pool or beach, right?
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Here is another example of how Society perceives things, and it isn't always the right outlook.
There was a case of Older Sister & Younger Brother Incest case around 2021-2022.
In it, the Older Sister had forced her Younger Brother to Incest
(as apparently the Sister was addicted to porn), which resulted in the Sister getting pregnant
(from what i remember, the Older Sister was around 13-14 when she got impregnated, while the Brother was around 10-11, and apparently the Sister had been forcing on the Younger Brother for years prior to that).
The end result, even though the Older Sister had confessed that it was her who had forced her Younger Brother into the relationship. It was the Younger Brother who got sent to the Juvenile, while the Sister got sent to Hospital for diagnosis of any foul play by the authorities. What happened after that was never revealed to the public though, as media got total silent on it.
The reason why the Younger Brother was convicted is simple.
It's because of the Societal notion that Women don't initiate Sexual relationship nor are they considered to be addicted to anything sexual related.
Aka., it is always the fault of a Male when such situation occurs, even if the main culprit confess it isn't taken into account.
And Media went silent on this case immediately because it was against the norm of that the Society is trying to set (aka., the fault was with the Women, which Society couldn't accept).