Correct, this is how we get "true breeding" lab mice/rat populations. They're essentially clones who get mated with each other, through specific and continual inbreeding. The genetic woes of inbreeding are massively misunderstood and, in most cases, overstated. Especially for sporadic instances of inbreeding.rockyoumonkeys said:To put it another way, if you created a family with perfect genes (no recessive defects), they could mate with each other nonstop without end and never have a defect baby. Not sure this is technically possible though.
Inbreeding is only a problem if there's a family history of genetic illness for practical purposes. The risk of having a child with defects increases after each successive generation of incest, but only if that risk was initially present. We don't have laws forcing people with similar "family histories" to get tested, or bar Askenazi's Jews from having children, despite knowing the risk[footnote]Due to the efforts of Askenazi Jews and with the help of genetic counseling, this problem has all but vanished in the U.S. IIRC most cases of Tay Sachs are now born to non-Jews.[/footnote]. Targeting incest specifically is pretty inconsistent and represents codified social bias.
One of my sister's friends married their step siblings who they met as pre-teens, I consider that pretty squicky. I wouldn't make it illegal though.