So, social libertarians out there-- which should be illegal?
A man marries his biological sister whom he was raised with and has two kids.
A woman marries her biological brother whom she was raised with, but one or both of them is sterile.
A man marries his adopted sister, who was adopted at age 3.
A woman marries her adopted brother, who was taken in at age 12.
A man marries his stepsister. Their parents were married when they were five.
A woman marries her stepbrother. Their parents were married when they were twenty.
A man marries his half-sister but one or both of them are sterile.
A woman marries her half-brother and they have kids.
A man marries his biological sister-- whom he was separated from at birth and didn't meet until adulthood. They have kids.
Same scenario as above, with sterility as a factor.
First cousins marry and have children.
First cousins marry and have no children.
An aunt and a nephew?
Where are the lines?
My outlook on it-- it should be illegal under all circumstances for two full-blood siblings who were raised together to marry and/or have children. People like that have clear mental issues and their kids would be messed up, physically from inbreeding and mentally as well.
If one or both proves sterility? Doesn't matter. Still the mental issue, potential for abuse, etc. Should they be jailed if they are incestuous? Nah. Order them into counseling and set up a restraining order to keep them apart.
What if they didn't know each other as children, though? If they met as adults? Well, this is rare enough that I figure that saying they can marry as long as they prove sterility first, for the sake of any kids. They weren't raised together. They may not even have known for a while. They're probably messed up a bit, but not the same as if they had been raised together.
I've always thought the guidelines should be:
-If they were raised in the same household since before one or both hit puberty, no marriage. Even if they weren't biologically related at all. If they weren't, then they should be able to marry. This wouldn't apply to large group homes or anything, naturally, only family situations where they are raised as siblings. There is a big potential for abuse there and on top of that to be attracted to someone whom you perceive as a sibling and have always perceived as a sibling is a sign of mental issues. Natural hormones developed from growing up in the same household should have made your siblings and parents seem sexually gross to you.
-If they are immediate family, full-blood or half-blood, or they are the aunt, uncle, niece, or nephew of their potential spouse, they should not be allowed to have children. Well, more specifically, they should not be allowed to marry unless they prove sterility, and if they have children they should not be allowed to raise those children themselves. Also, they shouldn't be allowed to adopt, because we really don't want whatever made them think this wasn't vile to get passed on to the next generation, and there's too much emotional baggage involved anyway. If there is sterility and the first guideline doesn't apply, they should be able to marry.
-If they are first-cousins, they should be able to marry as long as the first guideline doesn't apply. However, double first cousins-- ones that are cousins though more than one line-- shouldn't be able to have kids. North Carolina has the right idea with the distinction between double cousins and regular cousins, I think.
And of course all the laws should be made to include homosexual relationships, which should be treated the exact same way, only in all cases, of course, the sterility would be guaranteed, and they shouldn't be allowed to adopt. Two full-blood sisters shouldn't be able to marry. An uncle and nephew? Sure, as long as there's no sign of child abuse previously and both are of age. However, if your brother and your son want to get married, I think you need to seriously consider seppuku. Or at least a nice, comforting lobotomy and a change of identity.
And yes, the very thought of it makes me feel icky. Incest in any form to anyone closer than like a third cousin makes me feel icky (that's why it's nice that my boyfriend is a completely different ethnicity). It's gross. It's taboo. There is very little redeeming about it and it should be REALLY, REALLY discouraged by religions, parents, teachers, society as a whole... but that doesn't mean it should always be illegal. Laws should protect people from other people, protect minors from everything, and protect the mentally disturbed from themselves. So in many cases where there's a likelihood that it's not a case of mental issues, and there are no kids, there are no victims. It's gross, but then again, so are lots of legal things, like open-casket funerals, scat porn, rocky mountain oysters and Michael Jackson's face.