1. The source for this discussion between Rebbi Akiva and Rebbi Eliezer is the Mishnah in Nazir 7:4. The Tiferes Yisrael there (#36) writes that Rebbi Eliezer did not tell Rebbi Akiva the reason why one cannot construct a Kal va'Chomer from a Halachah l'Moshe mi'Sinai, but rather Rebbi Eliezer's source was simply that this is what he had received from his teachers. Rebbi Eliezer here was being consistent with his practice (see Sukah 27b) that he never said anything that he had not heard from his teachers.

2. We learn from this that the whole question is one of tradition. Even Rebbi Eliezer himself did not seem to know the reason for it, but we see from here how important is the issue of learning Halachos from one's teachers. Especially in the realm of deriving Halachos from verses, and even more so from the Halachos that were given personally by Hash-m to Moshe Rabeinu at Sinai, it is often very difficult for us to rely on our own logic, but instead we have to follow the way that was transmitted to us by Chazal.

3. In addition, we observe in the Mishnah in Nazir that when Rebbi Akiva was not told the reason by Rebbi Eliezer, he came to his other teacher, Rebbi Yehoshua, and repeated his argument. Rebbi Yehoshua praised Rebbi Akiva for his beautiful logic but concluded, in exactly the same way as his colleague Rebbi Eliezer, that this question is one that depends on tradition. Again, we see the importance of relying on one's teachers' superior experience even where one's logic seems to be sound.

4. See also the Gemara in Pesachim 81b, which also cites the exchange between Rebbi Akiva and Rebbi Eliezer. However, immediately afterwards the Gemara cites Rava who does learn from a Gezeirah Shavah. The Ramban, in his notes to the Sefer ha'Mitzvos of the Rambam, Shoresh 2, end of #30, writes that we see from here that even though one cannot construct a Kal va'Chomer from a Halachah l'Moshe mi'Sinai, neverteheless one can construct a Gezeirah Shavah from a Halachah l'Moshe mi'Sinai.

Kol Tuv,

Dovid Bloom