Over the years, I have accumulated an enormous amount of material on this topic, though I don't know if and when I will ever have the time to put it together; see too Isaiah Gafni, "Rabbinic Historiography and Representations of the Past," in The Cambridge Companion to The Talmud and Rabbinic Literature, and Akiva Weisinger's paper "Pre-Sinaitic Halakhic Observance As Interpreted By Medieval Authorities." Suffice it to say that both the maximalist view (that the Avos and their relatives were aware of the entire Torah, down to the details of disputes between the Shulchan Aruch and the Rama) and the minimalist view (that the Avos followed the will of God as it applied to them, but were not aware of commandments that had yet to be revealed at Sinai) have a long history of support among classical rabbinic authorities.
Should the minimalists mock the maximalists? I don't think that this is a good idea, for a variety of reasons. But I understand why it happens. It often stems from frustration that the maximalists are expecting everyone to accept their approach as the only legitimate approach, despite its inherent implausibility.
There are people who enjoy the intellectual gymnastics required to make pre-Sinai behavior conform with the Torah. There are people who actually seem to want Torah beliefs to be as fabulous, incomprehensible and counter-intuitive as possible. I once heard a wonderful person repeat a claim "from the seforim" that if one were to truly understand the spiritual depths of the trop (cantillation notes) of the Torah, it would be possible to figure out the words from the trop alone. Now, this notion is unreasonable to the extreme. But I received the impression that this person loved the idea precisely because it ran against all logic. The same goes for extreme Midrashim.
The maximalist/minimalist debate regarding the Avos keeping the mitzvos is somewhat related to the rationalist/mystical divide in two ways. One is that the notion of pre-Sinai people having knowledge of the Torah suggests the sort of supernaturally-sourced knowledge that is associated with the mystical school of thought. Another is that the rationalist approach prefers to minimize the extent to which beliefs run counter to reason; it seeks, to use Rambam's words, to harmonize Torah and rational thought as much as possible.
If someone wants to believe that Eisav and Yaakov were dealing with a shaylah in hilchos b'rachos, fine. They should be respectfully allowed to maintain such a belief. But they, in turn, should be sympathetic to those who do not wish to believe such things.