Perhaps Christianity was the faith of one's parent or grandparent, and although the individual does not particularly follow the faith, they were ingrained from childhood that God is the ultimate authority, and the Bible is God's instruction book to mankind.
Whether one truly believes in the Bible or not, it seems to have become a social standard to attribute one's own assumptions of right from wrong on scripture.
The general principle of this section is given in verse 6: Do not have sexual relations (the Heb. lit., “to uncover the nakedness of”) with any close relative other than your spouse.
To the contrary, all references to cousin marriage in scripture are 100% supportive.
This switch in cousin-marriage’s acceptance began in earnest in some parts of the Western world in the mid-19th century. Natural Selection himself, was married to his first cousin Emma Wedgwood.
Specifically, until the 1860s or so, first cousins commonly married in Europe and the U. Nonetheless, the practice soon fell out of fashion in the United States.
Although first-cousin marriages are legal in Britain, there have been calls to ban the practice because of reports that it has resulted in a higher-than-average incidence of birth defects in certain immigrant communities where it is common and culturally acceptable.
However, Professors Paul and Spencer said that the risk of congenital defects is about 2 per cent higher than average for babies born to first-cousin marriages – with the infant mortality about 4.4 per cent higher – which is on a par with the risk to babies born to women over 40.