“Anyone can be stringent merely out of doubt, whereas leniency requires a conclusion based on knowledge or tradition.” Rashi, commentary on Talmud Ketubot 7a

Kashrut exists on three levels: animals, their parts, and the mode of killing. The issue of animals is simple: “You shall not murder” applies to all species, with the exception of necessity for three or four animals. The common explanation is that the permitted animals have a quiet character; thus predator birds are not allowed. They believe that by consuming predators, humans change their character to predatory. The aborigines who ate Captain Cook held similar beliefs. Perch, a classical fish at the Jewish Shabbat table, is a predator fish. There are good arguments to support the view that the permitted animals are the least intellectually advanced.

In the absence of the Temple, the laws on admissible parts become unusable. In order to permit synagogues, an extra-Temple house of worship, rabbis interpret Jewish congregation as a Temple. If so, then we can reinterpret common Jews as priests; indeed, we were promised to be made a nation of priests. Thus, either allow common Jews the animal parts earmarked for priests, or ban synagogue worship.

The mode of killing may be wrong, but the only consequence is the transgressor’s guilt. The object of transgression, the wrongly slaughtered meat, doesn’t become inadmissible as food. Nowhere does the Torah say that incorrectly slaughtered animals become impure for use as food. Even had they acquired impurity, that in itself would not have prevented us from eating them, as impure byproducts of pure animals can be eaten, though the eater contracts short-term impurity (Lev11:40). The Torah is very sensible and doesn’t prohibit Jews from eating the three quarters of slaughtered animals which don’t conform to glatt kosher requirements. Now Jews hypocritically sell such non-kosher meat to Gentiles, but when we dwelt alone in the land of Canaan we could only throw away such meat, which was clearly not an option in a sustenance economy. The lawgiver was much more concerned about poor Jews than modern rabbis, who make the large families of religious Jews to live almost without meat, which is too expensive for them after all the kosher tricks are performed. So it is important to realize that modern kashrut laws, especially those of glatt kosher, are unrelated to the Torah and ancient Jewish practices. Erroneously believing the Torah and Talmud to be the same, many Jews ignore the Torah’s kosher laws along with rabbinical regulations. Rejecting the hypocritical and unnecessary kosher regulations, one should not reject the Torah’s laws as well—they are different categories. When you try to cheat on your taxes, it doesn’t mean you should disregard the sensible Bill of Rights as well.

It is especially odd to invent new and dubious prohibitions such as the one on oysters while disregarding explicit prohibitions in the Torah such as touching carrion. The same impurity is contracted by touching carrion and eating swarming things.