Yitzchak believed in Esav's ability to manage the material world morally and thus wanted to give him his blessing. Rivkah, however, knew the stark truth. In his present state Esav was not capable of advancing the world, since he himself was incorrigibly depraved. Perhaps after several thousand years of improvement, when the End of Days arrives, he will be fit for the task. He possessed strength, but it was the strength of wickedness which would be used for the destruction of the world, not it's advancement. Yitzchak saw the future ideal, and the absolute truth, in which Esav's strength must and will be employed for the world's benefit. Rivkah, however, saw the world in its present, realistic state where Esav was a source of evil. At present he is a murderer, as he said, "May the days of the mourning of my father come soon so that then I will be able to kill my brother" (Bereshit 27:41)." It is true that he was upset because his blessing was taken from him but there are limits even to an angry response. Wanting to hasten the death of his father was clearly above and beyond. It was even a bit too much for him to do personally, so he requested it of his dear uncle Yishmael, who would certainly comply willingly (Midrash Ha-Gadol, Bereshit 28:9). These murderous inclinations were not develpoed overnight because of a one-time event. They are indications of Esav's deep-rooted corrupt nature (Rav Charlop in Ma'ayanei Ha-Yeshu'a). Rivkah knew his present state better than Yitzchak and thus decided that in the meantime Yaakov would have to fulfill both his and Esav's tasks. Sarah had acted similarly a generation earlier when she decided to banish Yishmael from the home because of the negative influence of his corrupt behavior. Avraham was shocked. This went against the grain, which was the ideal of absolute kindness, but it was essential for practical considerations. Hashem confirmed Sarah's approach: "Do everything that Sarah tells you" (Bereshit 21:12). It is true that ideally they should live together, but at the present time it was not possible. "The events that occurred to our forefathers are indications of what will befall their descendants."