Many lands today actually display laws on the books that remain a kind of invasion of the modern world by the 3,000 year-old Mosaic legislation. Please remember, this silly stuff has the witch-burning mandates.
The modern world of genetics makes the “family-relative” sex laws obsolete, in terms of what damage one supposes might ensue. Since one can go to a clinic, submit a dna sample, and check in advance of a wedding one’s genetic compatibility with his betrothed, to make sure nothing bad (mutations, physical defects, etc) is likely to follow their union.
DNA restoring and editing technology will continue to make these obsolete as well, with innovations like CRISPR-Cas 9, a very advanced genome editor.
Ancient kings did in fact marry close relatives fairly frequently with little known material consequences (not too many physical defects of note). These can be obviated altogether today.
Moreover, the state is not allowed to prefer the faith of one religion over those of others in its legal codes, and these laws, especially given their obsolescence, clearly violate the separation of church and state.
Finally, the limits of “legitimate unions” set by these laws seems entirely arbitrary. There is no good reason to allow unions between “third cousins,” or more distant relations, but to allow second cousins; even weirder, forbidding one to marry one’s sister-in-law (the lady married to your brother, after he dies — assuming an untimely demise), makes no genetic sense whatever. She could be far more distant genetically than your 5th cousin, but she is disallowed. Huh?
Here, superstition should not be allowed to rule as law. The ancient Mosaic legislation must be removed from legal codes, and a better version adopted (if any) with the advice of medical specialists. Get real.
Likewise, Sunday and “Holiday” Laws should removed from all modern law.