For example, it seems that you assume that the post was arguing in favour of the most primitive moral relativism of "all preferences are equal" sort.

No, you've misread me. As I said, while the author accepts the presuppositions of moral relativism, he was busy climbing out of the relativist swamp to be able to assert his own values. He attempts to resolve the unease of the liberal moral relativist at the apparent contradiction between their avowed moral relativism and the assertion of liberal values.

It's a backhanded "tu quoque". Basically, yeah, we're forcing our values on people, but everybody does it. It's much like Doug Wilson's "tu quoque" defense of faith - rationality isn't self justifying, so reason is just "another faith". Everybody's doing it.

Both of these tu quoques operate by destroying the distinctions made by the concepts in question, faith and force. Just as no one believes that having faith that quacking like a duck will start your car is "the same" as relying on reason and evidence to use your key, no one believes that my desire to murder you is "the same" as your desire not to be murdered.

In his argument, he pits a conservative straw man and a vegan straw man against his relatively favorably portrayed liberal moral relativist. It's peculiar that you accuse me of straw manning Kaj, when his whole argument is based in contrasts to straw men he disagrees with, which is part of what allows him to blithely assert liberal values despite his admission that "we're no different than the conservatives".

Notice who's missing in his political universe? Libertarians - those who assert the difference between my desire to murder you and your desire not to be murdered. Yet another straw man aspect to his argument - those who would most strenuously object to his thesis don't even exist.