Killing is what some animals do to one another in the wild, maybe even their own species. Killing animals is something humans do for sport and as a food source.
Instead, I often think people who use that line of argumentation are trying to launder the feelings that listeners have towards murder into concern about their dietary choices at best, at worst they are working a rhetorical script in which they get to condemn those who disagree with them as murderers and therefore "win". In my own history, the people who don't fit that mold are willing to have a more nuanced discussion about what types of killing happen throughout the course of our lives, what makes a killing justified or not, how your stances change in a "survival situation" vs. the industrial killing that happens for most meat production, etc.
Saying humans have to die of hunger simply because humans cannot torture and then kill beings substantially like them in an industrialised manner is a disingenuous argument, and the reverse side of the same coin is basically cannibalism.
Murdering a mind that is substantially close to human’s (e.g., a dog) has been considered bad or even off-limits in many cultures for quite a while. Murdering human’s mind for whatever inessential purposes has been considered off-limits for longer (probably after we stopped with sacrificial murder). Morality progresses, news at 11.
"How morally bad a murder is depends on how close to human’s mind we’re talking about;"
Let's set aside that I don't think animals can be murdered -- My main disagreement with your point is that you don't speak to the mapping between "how morally bad" and "how close to human's mind"; IMO Reality has higher dimensionality and there is no linear ramp between the two. As one example, the morality of killing is weighted more heavily around whether or not I am in "community" -- for lack of a better term -- with the organism and the specifics of the killing rather than mind similarity. Killing spiders when it can be avoided is bad, but killing every last mosquito you get the chance to is good. For the most part, spiders make an area better for people, provided you don't fuck with them too much. Mosquitos always make things worse.
To further illustrate how I disagree with your response, let's consider something topical: Recently some dipshit got convicted for running an online community that bought and sold videos of the torture and killing of monkeys. Whether monkeys, cats, mice, octopi, fish, etc., soliciting the suffering and death of an organism for entertainment is pure evil, and likewise producing and profiting from such entertainment is pure evil. Hell, I still get a little uncomfortable when those cockroaches get bugstomped when watching starship troopers. I'm not saying the complexity of the mind doesn't factor, just that it ain't that simple by a long shot.
Guilt isn't necessary to be annoyed at someone's word choice. The chosen words are presenting an implication that eating animals is morally wrong, and if someone doesn't believe that and eats animals then they are right to be annoyed by the implication that they are acting immorally. No guilt necessary.
Or make them snappier two-liners, like you?
> they are right to be annoyed
Annoyed is an emotion. Someone's words triggered that emotion. Annoyance typically comes from someone's boundaries being crossed. One person might say, "Eh, murder/kill, whatever," but for some reason it triggered a deeper response in you. What do you think is behind that? You probably won't reply, but if you're a fan of metacognition, try tracing that emotion back by asking yourself why? every time you think you're done. Annoyance isn't a primary emotion, it is a response to one ore more. You have to be conditioned to be annoyed by words, unlike, say, mosquito bites. What makes you annoyed by it?