Have you met someone who claimed that their dog liked being slapped? When I imagine such a situation I imagine a person who is just excusing abuse because of the priors in my life, I have an easy time imagining this since I have encountered more than one such person. Impossible is probably too strong of a word, but I mean that you must interpret their behavior and interpretation is to me more a form of estimation not knowing, these examples are intended to show that non-verbal communication is still deficient when compared to a person with problems with verbal communications. Whether it is ok (ethical) to slap another individual that hasn't done anything to you is dependent on knowing their preferences and that takes communication and hence we apply our ethics based on communications.

"Insects die for carrots," is a problem for vegans who base their preference on the idea that killing any animal is wrong for sustenance. A person willing to kill a cow because they like the way the flesh tastes or finds it more nourishing simply isn't going to see a problem with an insect dying for a carrot. One person is holding themself to a higher standard and therefore is vulnerable to this critique. Animals need to die so that we may live, people quibble about where the line should be drawn but the line exists for almost everyone (excluding the Jain vegetarians, but practically speaking it exists for everyone).

I am not so much conflating those two as arguing that a) anti-specism much like freedom of speech has all kinds of caveats built in and isn't absolute even in the few people that would preach it, b) anti-specism doesn't form a basis for ethics because there are more absolute truths that override it but also render it unnecessary.