this is superconnected

Harm is, in my opinion, best defined in relation to pain and pleasure. Most simply pain is a state experienced as negative and worth avoiding; pleasure is a state experienced as positive and worth seeking. To cause harm is to, through one's actions, cause another individual pain (or loss of pleasure) by putting them in a situation or state that is (experienced as) less desirable than the situation they were in prior to those actions. Harm can be intentional or unintentional, but intentional harm is typically regarded as more significantly damaging and immoral. And in general, people agree that minimizing harm (regardless of intentionality) is a good thing, and, inversely, that causing harm (regardless of intentionality) is a bad thing. I think this idea of pleasure as good and pain as bad is very deeply rooted in our psychology as living beings. That being said, I don't know if it is the most accurate, practical, or ethical way to look at things. In my opinion, harm is a facet of human, animal, and natural existence that is inevitable and inescapable.

The simple act of feeding ourselves, for example, cannot be done without causing harm to the eaten. Hunting and killing an animal causes it fear and pain, and a significant reduction to its quality of life—in fact, one could easily argue that killing is the ultimate reduction to quality of life in removing that life altogether. Even if one tries to avoid harming more "complex" or sentient lifeforms like animals, plants and fungi do still have an innate striving to survive—therefore killing or damaging them in order to acquire food does involve causing a degree of harm to them. There is no way to sustain oneself without causing some degree of harm to other living beings. It is simply not possible.

Does this mean survival itself is unethical? In my opinion, no; rather, it means causing harm is morally neutral (with some qualifiers). Causing some degree of harm is acceptable, so long as the weight of that harm is equivalent to or lesser than the weight of the benefit it brings, and so long as we minimize excess harm to the best of our abilities.

A similar dynamic as above occurs within human relationships. We cannot always act in ways that maximize the pleasure of ourselves and everyone around us. Sometimes causing others pain is inevitable. Again, I think the conclusion we should reach from this is not that human relationships are intrinsically damaging and unethical; instead, it's that human relationships are complex and that harm is a natural feature that sometimes arises from that complexity, whether we want it to or not. Again I think we ought to follow similar rules as in the situation of sustenance—we shouldn't strive to avoid harm altogether, because that is futile, but rather we should try to weigh the harm with the benefit it provides while attempting to minimize that harm as best we can.