I've posted this many times, normally to obtuse responses about how "that only applies to Israelites" (kek, look at how race mixed jews are), but it always bears repeating

Ezra
>2 For they have taken some of their daughters to be wives for themselves and for their sons; so that the holy race has mixed itself with the peoples of the lands. And in this faithlessness the hand of the officials and chief men has been foremost.” 3 When I heard this, I rent my garments and my mantle, and pulled hair from my head and beard, and sat appalled.

The idea of "purity spiraling" is very biblical.