(I just lost about an hour's worth of thoughts on Cavell's essay. What follows will be truncated and written while grumpy.)
Cavell wonders whether it might be possible to "suffer" (p. 93) from a kind of blindness in respect to non-human animals, in the way that one can be blind to the humanity of other human beings. I think the answer is No. There might be kinds of mental handicap that make one incapable of seeing others as human beings, but otherwise failure to recognize someone as human, to treat them as a human being, is a moral failing. It is not something from which one suffers. Everyone knows that animals can, for instance, see, be sane, be loved, care for their young, fear for their lives, and so on. There is no therefore (...they have rights, or ...they should not be eaten, say), but the kind of blindness Cavell has in mind seems like a kind of bad faith, nothing more.
On p. 108 Cavell talks of different realms, seemingly meaning the human and the animal realms. He compares the difference with that between the human realm and the divine. I find this unhelpful, partly because I don't recognize any such thing as the divine realm. But also because, like Cavell, I want to acknowledge a host of differences and similarities between human and non-human animals. Talk of separate realms seems to downplay the similarities and make something like a metaphysical truth (something platonic or God's eye) of the differences.
He goes on to talk about the comparison of modern farms and Nazi death camps made by both Heidegger and Elizabeth Costello. He questions whether anyone not crazed could make such a comparison. I think they could. It's true that there are obvious and crucial differences, and that making the comparison risks insulting the victims of Nazi genocide. But ignoring the similarities also risks being insensitive to what they suffered. Remembering the Holocaust means (to my mind) thinking that we must never let such a thing happen again. And that means being alive to what is such a thing, perhaps even being extra sensitive to it. And feeling horror when we come across such a thing. Factory farms are not the same thing, but you don't have to be mad to find them too close for comfort.
Finally, on p. 122 and p. 124 Cavell talks about why he has not become a vegetarian, and connects this with the idea that vegetarianism is something like a self-righteous distancing of oneself from the rest of humanity. Orwell said something similar, I believe. This might be a reason not to insist that one's hosts go out of their way to serve one only vegetarian food. It might be a reason not to go on about one's vegetarianism. But I don't see how one could read Diamond's work, or Coetzee's (including works he has endorsed), and come away thinking that this is what motivates (or even constitutes) their vegetarianism.