There's a few other reasons why it's wrong other than just the "what if they have a baby thing"
siblings are supposed to help each other make it out in the world and start their own thing, do their
own thing etc. it limits ones ability to stretch out into the world if they end up married into their
own family (unless you're Royalty)
Note family tends to be overprotective and weird.
So if you're "that way" with your own family it ends up
being like a giant cult of sorts that you never get out of.
More often than not I think that feelings between brothers and
sisters or sisters and sisters bros etc tend to occur due to
rebellion against parents or bad abusive situations to begin with,
rather than an actual longing to marry ones sibling (not all the time but often)
Other times it's just that siblings find each other hot due to hormones
and getting turned on by everyone of the opposite sex (or the same) and this probly
happens to almost everyone at some point, however there is a certain built in disgust factor with some people
in regards to this as well. Just depends. Other times people get over the disgust factor.
Also, notice that when it comes to stepmothers and stepsons etc
in porn VERY often the theme is that the dad is not satisfying the mom
so the mom turns to the son for sexual help. Clearly that family has problems and should
probly just split up and start a new one somewhere else rather than resort to incest?
Note: I know there's exceptions to all these rules and there's of course
loving couples of all kinds who manage to make things work.
But let's speculate here.
Incest marriage defeats the entire purpose of being born to a degree,
you are supposed to eventually leave your immediate family or surroundings,
if you stay in the same spot you were when you were born, why even be born?
That said, yes stepsibling and stepfamily porn is popular right now.
That's cuz no one can get laid, duh. It's a bad sign.
That says something about how far we've slipped in our society, lol.
If stepfamilies etc. experiment now and then, meh, not that big a deal,
and it might actually be healthy (if done safely).
But incestual marriage just confirms the entire slippery slope
argument of the right. And next comes "safe" bestiality and everything else.
When it comes down to it civilizations often collapse when sexual activity
becomes the most discussed thing. It's because a lot of people are just
apparently naturally predisposed to being opposed to free love or
certain types of sexuality (which might be a shame but just is true)
So when you make every type of behavior the center of discussion
you always have the sex positive people and the sex negative people
and it's always a divisive thing. Certain types of behavior always
will offend someone and it doesn't mean the opposition is necessarily
hateful. It's like if one guy likes garlic and the other guy doesn't
he'll ALWAYS find it disgusting.
You keep things to a minimum and have at least a small degree
of standards or everything eventually goes to pot. I wish it didn't work that way. It does, sorry.
However, I dislike prudes myself. Not even a huge fan of traditional values.
But upfront sexual deviance mostly just creates more prudes ironically.