This is a tricky one. Of course there are biological and genetic reasons why incest is 'wrong' but in the modern age of contraception, whereby we can be pretty much guaranteed that intercourse will not result in pregnancy if we are careful, this is now a smudgy issue.

I'm pretty sure that most people would still see it as 'wrong' but as for why that is, there really isn't a clear answer.

If it isn't causing anyone emotional distress then fair enough, although it's worth remembering that a relationship like this could not lead to marriage or children and that perhps both parties would benefit from looking further from home for their sexual partners.

I may even be a little concerned that someone who is so attracted to a sibling may have some deeper problems when it comes to forming attachments outside of the family group which might warrant further investigation/assistance. . .

I'm afraid that's as much as I can contribute seeing as I have never felt sexually attracted to my sister (much to her current boyfriend's disappointment, as we won't agree to a threesome!Lol)

Well you did ask!!!

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'Don't knock masturbation - it's sex with someone you love'

- Woody Allen