The Torah underscores that Avraham and Yitzchak were father and son. One would think this is a confirmed verity and does not require the Torah’s reinforcement. Apparently, as Midrash Tanchuma (quoted by Rashi) posits, the leitzanei ha’dor, cynics of the generation, intimated that Sarah Imeinu actually had become pregnant during her short captivity in the home of Avimelech, so that Avraham Avinu had not fathered Yitzchak, but actually, Avimelech had fathered him. Therefore, Hashem made Yitzchak’s features so undeniably similar to Avraham’s that no one could doubt Avraham’s status. Two questions glare at us: Why were these scoffers referred to as leitzanim, cynics? They were out-and-out reshaim, wicked! Second, what is the meaning of the appellation leitzanei ha’dor, cynics of the generation? If they were simply leitzanim who degraded Avraham, it would be sufficiently evil. Why must they be, so to speak, the cynics of the “generation”?
Horav Moshe Feinstein, zl, derives from the first question that a cynic is worse than one who is wicked, because one is able to maintain an intelligent dialogue with a wicked person and even, perhaps, transform him by inspiring him. The wicked person listens. The cynic is much worse. He degrades everyone, makes a joke of everything. As Rav Moshe explains, the leitz is not machshiv, does not consider, anyone to be worthy of himself. It is impossible to achieve anything in a conversation with someone whose condescending attitude is the product of a jaundiced view of life. The cynic thinks that he is smart, but, by his very actions, shows otherwise. He lives a life of self-imposed blindness, negativity, with a driving desire to pull everyone else down into his abyss of acrimony.
With regard to the second question, why they were called leitzanei ha’dor: I think their goal was not simply to debase Avraham, but everything for which he stood and represented. Chazal speak about ten generations from Adam to Noach, followed by ten generations from Noach to Avraham. Our Patriarch was on the verge of altering the downward trajectory of the previous twenty generations. These cynics sought to impede his ability to do so. They sought to employ their cynicism to maintain the downward trend of the generation. Avraham’s calling out in the Name of Hashem, reaching out to the world to proclaim His Glory, interfered with their nefarious success.