Most of the other problems I mentioned are about being raised or growing together. So in your example, it probably would be mostly fine.
My main point is, what does it bring to try to make exceptions when the only exceptions that are not bad are very, very unlikely, and do not bring anything more than any other relationship would?
In your case, sure, the two sisters could get together, fine. But if they got together while knowing they are from the same family, it does raise a weird point, and if they did not know then fine. But how many offspring-free relationships between two people that didn’t know they were related, exist? How many of those last? I cannot imagine such a big proportion, so what is the point of making an exception, that on the other hand will bring in a lot of problems and creepy behaviours trying to fit in it.
Most of the other problems I mentioned are about being raised or growing together. So in your example, it probably would be mostly fine.
My main point is, what does it bring to try to make exceptions when the only exceptions that are not bad are very, very unlikely, and do not bring anything more than any other relationship would?
In your case, sure, the two sisters could get together, fine. But if they got together while knowing they are from the same family, it does raise a weird point, and if they did not know then fine. But how many offspring-free relationships between two people that didn’t know they were related, exist? How many of those last? I cannot imagine such a big proportion, so what is the point of making an exception, that on the other hand will bring in a lot of problems and creepy behaviours trying to fit in it.