I’m not sure what to think. Incestuous relationships are problematic. From what I understand, only brother-sister procreation is a problem, in terms of mental problems in the children, and that only over many generations. That is, consistent inbreeding is a problem, but if it happens only every once in a while, it is much less of a problem.
But then this gets to the issue of whether sick people have a right to life. A lot of people seem to think that they don’t want to bring a child with a certain level of chronic illness into the world. Perhaps a brother-sister relationship might feel the same, and do genetic testing in time to have an abortion, if necessary.
Then again, it seems to me that if you ask the person who has chronic illness whether on not they wish their parents had never had them, very few would actually wish to never have been born. Most people would rather have a chance at life, no matter how hard it is. And even this is subject to how one is raised to view life. A person raised to appreciate life is going to probably appreciate it more than a person raised to think only a certain kind of life is acceptable.
Then there’s the ick factor. This is the knee-jerk reaction that many of us have been raised to have about certain kinds of relationships. Many people have that reaction to homosexuality, and of course to incest. What is that about? Is that cultural or is it inbred? I think there’s something about living with someone from birth that makes us feel like they are too close and they know us too well to want to be intimate with. But clearly this isn’t the case for everyone.
The other think about incest is the possibility of abuse issues. Usually the power relationship is such that it is not clear that a brother and sister could enter into a truly consensual relationship. In fact, I bet many psychologists would say that an incestuous relationship can not be psychologically healthy and therefore should be outlawed, so that no mistakes get made. To my mind, this is the most powerful argument against incest, but even it is not necessarily a valid argument in all cases.
Finally, this question raises the “gay issue.” That’s irrelevant to my mind. Incest and homosexuality have nothing to do with each other. Their only possible relationship is that they have both been (or still are) taboos in many cultures. Other than they both have been taboo behaviors, there is no logic to link one with the other and any connection is extraneous and—dare I say it—trolling behavior.