http://revach.net/article.php?id=4186

Section: Parshas HaShavua   Category: Quick Vort
Parshas Vayeitzei - Maskil L'Dovid - Was Yitzchok's Talmid Elifaz An Am HaAretz?
Rashi tells us (Vayeitzei 29:11) that Elifaz came to kill Yaakov on thee command of his father Eisav, but since he was a talmid of Yitzchok he was hesitant and agreed to Yaakov's solution of taking all his money thereby technically fulfilling his father's command.  Was Elifaz the Talmid of the Gadol HaDor Yitzchok such an Am HaAretz that he didn't know that the halacha says if your father tells you to do an aveira you need not listen, murder no less? 

The Maskil L'Dovid answers that Elifaz only listened to his father because it was Pikuach Nefesh.  Eisav threatened to kill him if he doesn't kill Yaakov.  Even though murder is Yaharog V'Al Yaavor and one must die rather than commit murder, this is only for a Yid who is chayav in the mitzva of Kiddush HaShem.  However Bnei Noach who have no mitzva of Kiddush HaShem, are exempted from any aveira under the threat of death, even murder.