Jews altered the Noahide Laws to allow Parsis to commit first-degree incest

See Table Of Contents Here

All it takes is one drop of poison

https://books.google.com/books?id=9pc0CwAAQBAJ&pg=PA61#v=onepage&q&f=false

Kiel, Yishai (2015). "Noahide Law and the Inclusiveness of Sexual Ethics: Between Roman Palestine and Sasanian Babylonia". In Porat, Benjamin (ed.). Jewish Law Annual. 21. Abingdon, Oxfordshire: Routledge. pp. 61–63. ISBN 978-0-415-74269-6.

Alongside this legal-theoretical interpretation of the differences between the two Rabbinic centers in terms of natural and positive law, the study puts forward a contextual-cultural reading of the data. This reading situates the Palestinian Rabbinic approach in the context of Greco-Roman and Christian rhetoric, and the Babylonian Rabbinic approach in the context of the ambient Iranian culture. In particular, it focuses on the significance of Pahlavi (Middle Persian) literature for a more nuanced and contextual understanding of Babylonian Rabbinic discourse, by examining the Babylonian Talmud's treatment of the sexual prohibitions in light of the well-attested Zoroastrian doctrine of Xwedoda.3 Although the original Avestan meaning of this term is somewhat unclear,4 in the Pahlavi sources xwedodah is said to refer to endogamous marital unions, especially between father and daughter, mother and son, and brother and sister, and is considered one of the most pious and laudable deeds in the Zoroastrian tradition.5 

Adducing the Greco-Roman and Christian writings on incest, which generally promote universal standards of sexual conduct and explicitly condemn Iranian deviation from these norms, as we will see below, sheds light on the Palestinian Rabbinic advocacy of inclusive standards of sexual ethics. On the other hand, we can shed light on the Babylonian Talmud's espousal of exclusive, particularistic sexual norms, and relatively tolerant approach to non-Jewish incest, by adducing the Zoroastrian practice of xwedodah and the related doctrine of moral relativism expressed in the Pahlavi literature. I will argue that the Babylonian Rabbinic discussion of Noahide sexual prohibitions invokes certain legal and theological considerations found in the Pahlavi discourse. 

While it is likely that the Babylonian Rabbis witnessed the practice of next-of-kin marriages, and that this in turn influenced their approach to doctrinal issues pertaining to incestuous unions, the Babylonian Talmud does not simply respond to the practice of next-of-kin marriages during the Sasanian period.' I contend, rather, that the Babylonian Talmud actually engages with important strands of contemporary Zoroastrian discourse on xwedodah, discourse preserved in the Pahlavi corpus. 

To be sure, the Babylonian Rabbis had no wish, nor were they in a position, to challenge the sexual restrictions listed in Leviticus 18 and 20 (which strictly forbid intercourse between first-degree relatives) insofar as Jewish norms were concerned.8 The prohibitions against incest and certain other sexual unions were widely accepted by the post-biblical traditions, Rabbinic and non-Rabbinic alike, and could hardly have been challenged by the Babylonian Rabbis. Nevertheless, I will demonstrate that alongside the prohibitions that are applied to Jews, the Babylonian Talmud voices novel, often subversive stances on incestuous relations among non-Jews, tolerating such relations to varying degrees. Unlike other non-Zoroastrian discussions of incest, which, for the most part, are polemical and critical, the Babylonian Talmud's approach to next-of-kin partnerships is nuanced and complex. Although occasionally polemical,' the discussion in the Babylonian Talmud is far less critical of the practice of Incestuous unions among non-Jews, and even seems to engage with certain key rhetorical and doctrinal arguments made in the Pahlavi writings.