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Apparently, there wasn't a flaw in what he said, since it is quoted by the Poskim in various places; see, for example, the responsa of Rav Eliyahu Mizrachi (#81) and Tzitz Eliezer (12:15), who use the Gemara as proof for Halachic purposes. However, since Rebbi Eliezer enjoyed the fact that a Min had expounded the Torah, he was fascinated by the way in which the Min learned and may have heard other interpretations from him which would vindicate his religion. The implication is, as with the rest of the Sugya, that "Minus" (probably referring to Christianity) has an attraction and can ensnare innocent Jews who will not be able afterwards to restore their faith.

Does this mean that we cannot learn from an Apikorus? This is a broader discussion dealt with in Chagigah 15b at length. The conclusion is that only a person of Rebbi Meir's caliber is capable of studying from an Apikorus, since Rebbi Meir "found a fruit and ate the inside and threw away the peel," meaning he knew how to separate the good from the bad even in the teachings of an Apikorus. How, then, did Rebbi Eliezer blame himself for having learned from a Min, since he was undoubtedly a great man himself? It is possible that he disagreed with Rebbi Meir, but perhaps we could explain this according to another statement of Rebbi Eliezer. The Gemara in Sukah relates that Rebbi Eliezer "never said anything he had not learned from his Rebbi." Rebbi Eliezer was very meticulous to transmit the traditions of his teacher, Raban Yochanan ben Zakkai, and no other tradition, in order to maintain the purity of the oral tradition. Hearing other interpretations from impure sources and enjoying them may distort this purity, and, therefore, Rebbi Eliezer was so stringent with himself.

Yoel Domb