True Left

"Then why accept Abel's sacrifice and not Cain's, given that Cain was the one following the supposed instruction to be vegan and Abel was the one who wasn't?"

Yeah, this single passage alone utterly destroys the notion that the Tanakh could endorse veganism. The fact that Cain was only punished AFTER having killed Abel is proof enough that "slaughter-based sacrifices are the most sufficient" was one of the core messages of that section of the Tanakh. Cain was already looked upon less favorably even before he had done anything "wrong"

"Stop assuming they are sincere in anything they do!"

As a collective identity, I agree that they absolutely cannot be trusted to be sincere. However, on a more individual level, I do think that there are genuine false leftist Jews that adopt veganism (or anti-racism, or anti-homophobia) for ethical reasons and yet misguidedly cling onto Judaism and even support Israel directly or indirectly. There's definitely some animosity between Jews in different political camps, and I think that's natural since no group is immune from fragmentation or dissention. Not even Yahweh's favorite tribe can be entirely cohesive at all times. I'm not saying that there aren't Jews who co-opt beliefs and identities (including veganism) so that they can control both sides, but I think it's more helpful to distinguish between false left Jews, and the orthodox Jews (who may or may not hide their orthodoxness, depending on the tactics they choose). My issue with the Orthodox Jews is that they're following true-to-form Judaism, and my issue with the false left Jews is that they fall into all the trappings of the false left while also ultimately benefiting the orthodox side, whether they know it or not, and whether they actually want to or not

"'Ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him.' - Jesus"

This quote describes the Devil, and I agree that our view of the Devil's nature should be uncompromising since I'm an absolute dualist, but for those within the material world and subject to the Devil's whims, I think that it's possible to have God speaking in one ear and the Devil speaking in the other. False left Jews suffer largely from the same problem that non-Jewish false leftists do: something within them is telling them to do the right thing, but the Devil is ultimately speaking louder, and some of his temptations are too enticing. Hence why they possess enough good sense to question the dynamics between humans and non-humans, and even ethnic discrimination, but not enough of it to do away with creator worship and adopt Gnosticism

Thanks for your input on the topic, by the way