> if scientific evidence can tell you that your marriage to your first or second cousin is highly unlikely to cause genetic defects in offspring

The science is not there. It probably will never be there. We can only screen for certain conditions. Close marriage will turn up all sorts of new conditions no one knows about (ahead of time).

Until the day we can make our DNA "perfect" close marriage will always be a problem.

And on that day I suppose even sibling marriage (or incest) would not be a genetic problem.

You're correct in that you can only test for things you know about (duh, you don't know what you don't know) so as far as screening goes, it's just a matter of how much you're screening FOR. It's also really easy to rule out which diseases are not likely to occur just by checking one person's DNA. You only have to screen where both samples can potentially combine to form something bad.

Far from all hereditary disease are easy to rule based on genetic tests.

You need to differentiate between Mendelian and Complex genetic disorders. While genetic tests are useful to indentiy disease caused by a single allele (Mendelian disorders), they today are inconclusive for many other Complex diseases, like rheumatoid arthritis, with a known genetic component. These disease are multifactorial: the interplay between several genes (variants) and environmental stimuli cause the disease. One of several genetic mutation must be present for the disease to occur, but without an environmental stimulus, the disease will never materialize. As such, even though we have acces to a full genom sequence, genetic tests are inherently limited and thus inconclusive in determining risk for many diseases.

Over a long time? Maybe. But it won't happen overnight. In most cultures that taboo is cemented. Ask any random person who think it's taboo why it's taboo and I would wager they don't really know why, just that it is. As such, I don't think this is going to change minds, at least not for a while.

> they don't really know why, just that it is

This taboo does not come from the Bible, since the Bible does not prohibit cousin marriage. I assume the taboo comes from seeing problems in offspring.

Scientifically, occasional cousin marriage is not usually a problem. It's only when it's repeated more than once that it starts to be a problem.

I made no mention of the Bible nor where the taboo comes from, but merely mentioned that is is a taboo that is cemented in some cultures and I posited that most people from those cultures aren't aware of why they think it's taboo beyond the fact their culture makes it taboo.

I know you didn't. But a lot of people falsely think it comes from the Bible, so I figured I'd mention it.

The cultural resistance to cousin marriage is already an overreaction to just the statistical odds of genetic diseases, without any screening.

(Part of the explanation is that humans are not particularly genetically diverse overall)

At that point you begin down the slippery slope. Most people would be repulsed by the very idea, but down the road who knows. "Culture" does indeed change. That said, I don't see being able to overcome the gut reaction.