Many steps can be taken to avoid conception such as condoms and diaphragms and even pills
None of which have a 100% success rate. My latest child was conceived 7 days before I was sterilised, and we were using condoms. There are factors which can affect the success of oral contraceptives too. In short, if you are not sterile then you CAN get pregnant.
and even if an incestual couple manages to conceive, then abortion is always an option (yes I'm pro choice).
If you are pro-choice then this surely means you respect the choice of the brother and sister to NOT have the abortion, right?
And even if then, the chances of birth defects from incest is no more higher than birth defects coming from mums who drink, smoke, or take drugs during pregnancy.
This isn't about not wanting disabled babies in society, it is about avoiding increasing the levels of genetic diseases within the species. Which in the long term brings about a higher level of unnecessary suffering.
Also mothers over 40 also have high chances of birth defects. Also people with born disabilities or inherited diseases have high chances of birth defects. Yet nobody ever makes a big deal about these people procreating, but for some reason when they a hear a sibling couple who merely want a childless relationship, they always shout out "BUT THINK ABOUT THE BABY"
I think you have completely misunderstood. At no point did I say that sex with siblings should be prevented, I just said that from an objective point of view humans find it immoral (undesirable.) I think anyone in a position of having children with a high risk of genetic diseases should consider it very deeply before deciding to continue.
The thing with immorality is that things become exponentially "more" immoral when more people do it. A relatively small number of babies being born with genetic deformities is not going to be significant to our species in the long run, however if our species were to start incestuous relationships on a large scale then it would be far more significant.
I really see it as one of those laws which is there to tell people "society finds this wrong" which really shouldn't be enforced. We shouldn't be putting siblings in prison. It's all about using some common sense. We KNOW that this practise increases suffering in the world so we should accept that it is not something we should promote as "normal", but it is not significant enough to be punishing individuals for.
My point about homosexuality was that there are no third parties involved at all.
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