Starting in Genesis 12:13 Avraham and Sarah deceive Pharaoh into thinking that Sarah was not married. It seems from the verses that Avraham and Sarah understood that if Pharaoh thought Sarah was unmarried he would take her as a consort. My question is, given that adultery is one of the seven Noahide laws and one of the 3 transgressions for which one must give up one's life rather than violate, for what reason or by what right did Avraham and Sarah perpetrate this ruse? Shouldn't Sarah, under fear of rape/adultry have disclosed her relationship? And, shouldn't Avraham allowed himself to be killed, or perhaps at least wait until his life was threatened, before putting Sarah in that predicament?
The Zohar (part 1, 81b-82a) says that Avraham saw the Shechinah with Sarah, and therefore knew that she'd be safe:
רַבִּי יֵיסָא אָמַר יָדַע הֲוָה אַבְרָהָם דְּכֻלְהוּ מִצְרָאֵי שְׁטִיפִין אִנּוּן בְּזִמָּה, וְכֵיוָן דְּכָל הַאי יָדַע אַמַּאי לָא דָחִיל עַל אִתְּתֵיהּ דְּלָא אַהֲדַר מֵאָרְחָא וְלָא יֵיעוּל לְתַמָּן. אֶלָּא בְּגִין דְּחָמָא שְׁכִינְתָּא עִמָּהּ:
And the Midrash (Vayikra Rabbah 32:5) adds that her experience there enabled the Jewish women during the Egyptian exile to be protected from arayos:
רַבִּי הוּנָא בְּשֵׁם רַבִּי חִיָּא בַּר אַבָּא אָמַר שָׂרָה אִמֵּנוּ יָרְדָה לְמִצְרַיִם וְגָדְרָה עַצְמָהּ מִן הָעֶרְוָה, וְנִגְדְּרוּ כָּל הַנָּשִׁים בִּזְכוּתָהּ.
Rav Hirsch explains on Lech Lecha 12:13 that they were actually in less danger this way than if they had admitted that they were married.
After all that occurred in Egypt and in the land of the Philistines we can conclude that - to which European countries in our modern times may not be without analogy - virgins, unmarried women were more protected against the prevailing immorality than married women. And add to that, a stranger! In both cases, married or unmarried, Sarah's honour was in danger. But, as a married woman the danger would be imminently threatening. One simply kills the objecting husband and rapes the wife. In the case of an unmarried girl accompanied by her brother one hopes to get her through the favor of that brother. In any case this way takes longer, postpones the matter, and in the meantime Hashem can help.
The Egyptians (even the nobles) would have thus, restrained themselves while they tried to get Avraham to agree. Once Par'o expressed an interest, they would have withdrawn and been careful not to offend someone that Par'o wanted to favor. Avraham was successful until Par'o decided to stop playing around and kidnap Sarah.
If Avraham had not taken this tack from the beginning, he would have been unable to make the claim later.
The point Rav Hirsch is making is that one is allowed to take steps in order to avoid being forced into a position of יהרג ואל יעבר. In the way the culture of the time behaved, what he did was to prevent them from being faced with rape/adultery in the first place. Even after she was kidnapped and taken to the palace, Par'o first tried to appease Avraham. Then Hashem intervened so that Sarah was never placed in the יהרג ואל יעבר situation.
This is addressed by Ralbag in his commentary there:
התועלת השלישי הוא ג"כ במידות והוא שכשיביא ההכרח שיגיע הרע לאדם מהראוי שיסתכל האדם באי זה אופן יתכן שיגיע לו יותר מעט מהרע ויבחר בו ולא יתרשל מזה מפני הרע שיקרה לו כי ראוי שיהיה נבחר הרע היותר מעט לברוח מהרע הגדול ממנו הלא תראה שאברם בחר לרדת לארך מצרים לברוח מהרעב שהיה בארץ כנען ואע"פ שהיה נכון המקום ההוא אל שיקרה לו מהגנות שתתגאל אשתו בזימת הארץ וראוי שתדע שלא היה בזה חטא לאברם כי שרה תעשה באונס מה שתעשה מזה ולזה לא תאסר לבעלה אפילו אחר נתינת התורה כמו שאמרו ז"ל באסתר קרקע עולם היתה ואם היה אברם בוחר סבל הרעב אשר היה אפשר שימות בו על סבל מה שאפשר שיקרה לשרה מהגנות היה זה חסידות של שטות כאמרם בשלישי מסוטה היכי דמי חסיד שוטה כגון דחזי דטבעה אתתא בנהרא ואמר לאו אורח ארעא לאצולה ולאיסתכולי בה
The third lesson is also in character traits. And it is that when circumstances force that evil will reach man, it is proper for the man to look which way has the possibility of less evil and choose that one. And he should not give up on this on account of the evil that will happen to him, because it is proper to choose the lesser evil to escape from the greater evil. Do you not see that Abram chose to descend to the land of Egypt to escape from the famine that was in the land of Canaan, even though that place was predisposed to the occurrence of the degradation that his wife be sexual in the promiscuity of the land.
And it is proper that you should know that there was not a sin for Abram in this, because Sarah did what she did under coercion and would therefore not be forbidden to her husband even after the giving of the Torah – as the Sages say about Esther that she was like mere ground. And if Abram had chosen to bear the famine, in which it was possible for him to die, over bearing the possible degradation that could happen to Sarah, it would be piety of foolishness. As [the Sages] say in [Chapter] Three of Sotah: "What is a pious fool? For example, he sees a woman drowning in the river and he says 'it is not the way of the land to save her and look at her'."