I think something we shouldn't forget, that Huemer mentions, is that a lot of these arguments against anarcho-capitalism happen from the state of nature starting point. However, Huemer points out that given things have been pretty much set up now, we can start taking that final step to make the freest society and transition to anarcho-capitalism. So, the transition isn't from state of nature > ancap, but statehood > ancap, which is a lot more plausible. Indeed, it's also realistic, since in the actual world, there are already states, not states of nature.

Granting Huemer is right on metaethics, he doesn't give a good reply to cultural biases in our intuitions.

Which reply do you have in mind?

For one, I think his observation that there really isn't that much disagreement in the first place about our ethical intuitions is a strong argument against the cultural bias argument. That is, it turns out that culture really doesn't seem to affect our ethical intuitions (in the same way they don't seem to strongly affect our visual perception); they are pretty stable universally.

This might sound insane when you think about all the alleged moral disagreements there are, but Huemer is quick to point out that these aren't moral disagreements but just factual disagreements. For example, we might say that culture affects our ethical intuitions about infanticide (cf. the Aztecs), about abortion (cf. Christianity), or about a host of other issues. But as Huemer points out, none of these disagreements are a result of divergent intuitions; they are about divergent facts: e.g., whether fetuses are persons, as opposed to whether it is wrong to murder innocent persons, the latter which is a moral intuition that is shared universally.