This is simply not accurate. Or rather, it's partially accurate, and it's only part of the story. The increase in risk isn't huge, and the amount it happens effectively leads little to be concerned about.
"Contrary to widely held beliefs and longstanding taboos in America, first cousins can have children together without a great risk of birth defects or genetic disease, scientists are reporting today. They say there is no biological reason to discourage cousins from marrying."
"'In some parts of the world,' the report says, '20 to 60 percent of all marriages are between close biological relatives.'"
"Dr. Motulsky said researchers did not know why marriage between cousins was viewed with such distaste in the United States. He said some of the revulsion might have stemmed from the eugenics movement, which intended to improve the human race by deciding who should be allowed to breed. The movement flourished in this country early in the 20th century." [1]
https://www.nytimes.com/2002/04/04/us/few-risks-seen-to-the-...
Probably isolated areas, like small islands or remote settlements in the wilderness where there is not much to choose from.
I've lived a year in such a place and, while there weren't genetic illnesses that I was aware of, I wouldn't use that place as evidence of how inbreeding is innocuous. Let's leave it at that.
So you... didn't see any genetic issues, thought that they were sub-par humans, and are blaming inbreeding? That's not a great look on your part.
I suggest we stick to studies and data, and leave it there instead.
But that's only relevant to the immediate offspring. A single generation of outbreeding reduces the level of inbreeding to zero. So if you see a cousin marriage several generations back... so what?
I see that as a common claim, but given the lack of similar concern to non related individuals with recessive genetic disorders, even in cases where both parents have it, or in cases where parents have dominant genetic disorders, I find myself seeing this as a more after the fact rationalization than the actual reasoning. And as for the actual increase it risk, it seems quite minor compared to many other behaviors that increase risk which society doesn't frown upon nearly as much (with drinking and drug use being the notable exceptions that are routinely condemned).
Nope, if both parents have the gene and neither has the disorder (e.g., both are heterozygous), offspring will get the disorder 1/4 of the time, be a carrier half of the time, and be clear 1/4 of the time.
If both have the disorder, the child will also have the disorder, but that's usually not the concern.