I recently saw this topic on student room. I scrolled a few pages and it's filled with weak defense or just pure hate speech, then I contemplated and realised why homosexuality is completely different from incest. Let's breakdown things case by case to see it.
Firstly, we are talking about the love between a SINGLE mother and her son or a single dad and his daughter, or brother and sister,because if they are still married, then it's simply adultery and it's wrong because love without loyalty is just lust.
Secondly it's a difference of nature of the topic, straight incest is different from homosexuality is because... What's the difference between your mother and another woman of her age. OK, maybe you two been through things together, but except the fact she gave birth to you(note same applies to father daughter situation) which is something to be grateful rather than for you to find attraction in them because of it. What is it, that is different between you mum and every other single mother, I argue, not much. While for homosexuality, if you like man, there isnt a woman that's also a man, (note I did not say someone can't be both, that's another issue, I am saying if you are strictly identified as a woman, then you are not a man.) So that's a big difference.
Then, someone would say, OK, just because they can change, they should? No. That's just to clarify why incest is NOT a sexual orientation. But the problem comes to, once a boy married his mum, then there is a double relationship going on, one where he will have intercourse with his mother and love her that way and one where he have to respect her and have a completely different type of love. The two are contradictory to each other at its very core. Thus it would not be Ok and completely different from homosexuality.
Finally the question about brother and sister incest, well, to be entirely honest, it is not a wrong thing, unless someone can raise a point against it
...for the 2nd time this year