Recently I read a book called River of Stars, by Spencer Scott. It's a good book overall, but some of the narrative choices didn't seem to have been particularly well-thought-out, and that prompted me to consider similar societal blindspots. The book series revolves around interactions between humanity and various species of aliens; the three species most relevant to this post are the Aa'gimli, the Torzek, and the Li'farai'i.
The Aa'gimli mostly only come up in reference to past events. They were the first species to meet humanity, though the reverse was not true, and they initially mistook humans for non-sentient creatures, allowed the consumption of humans, which were an unusually efficient nutrient source, and ignored evidence that this was a mistake.
The main conflict of the book revolves around a similar mistake, this time made by humanity; the Torzek inhabit a planet extremely unusual in being both inhabitable by humans and nearly free of bitoxiphosphene (since most species aren't affected by it, they tend to never have placed restrictions on its release, and their atmospheres are substantially more bitoxiphosphene laden than our own). Humans make an attempt to determine whether Torzeks are sentient, but find no evidence of communication, tool use, or even motion. They conclude that they most likely are not, and begin killing them indiscriminately to make room for human colonists. However, in fact they are sentient, and just as intelligent as people; though rooted in place, they are in fact capable of higher-level reasoning on a level matching humans, and they turn out to have chemical-based communication of equal complexity with any human language. The story revolves around a few humans who managed to determine this attempting to prevent further murder.
My objection, then, is to the portrayal of the Li'farai'i. We are repeatedly shown allegedly-sympathetic characters, fully aware of the situation with the Torzek, remarking on the Li'farai'i as an obvious example of non-sentient creatures. On multiple occasions, two of the characters play a game involving shooting them for target practice. When Abibel displays empathy towards one of them, this is portrayed as naive, the result of her being eight years old.
The problem here is that they do not have enough information to conclude that the Li'farai'i aren't sentient. Perhaps they are correct, but if so it is because of luck, not because they behaved correctly. It may not be clear that they are, but in cases of uncertainty with stakes so high, it's better to err on the side of not committing murder.
Now, I'm not saying that we ought to be concerned that trees or water molecules or smartphones are secretly sentient. But when we wonder how people managed to conclude that other humans weren't people, we ought to keep in mind how often people err on the side of assuming they are not. We don't know for certain when fetuses start to be sentient, but that doesn't mean we should conclude that it is ethical to indiscriminately kill them, and the fact that being pregnant causes some harm to the mother does not change that. Opposing abortion doesn't require belief in God. It simply requires applying the heuristic that if there is any uncertainty about whether someone is a person, we should assume that it is when deciding whether to kill it.
It's easy to look at others and say that if they had only used such an obvious criterion, they could have avoided literal murder. It's harder to apply the same criterion to ourselves, but that in no way diminishes our obligation to do so.
