Sorry for the delay. - I should have been more precise. I'll provide more precision by commenting on the cases you mention:

• The injured pet case probably involves three complications: (1) people's belief that it's an "egoistic" case for the pet (instead of it being an "altruistic" trade-off case between pet-consciousness-moments), (2) people's suffering that would result from the death/future absence of the pet, and (3) people's intuitive leaning towards an (ideal) preference view (the pet "wants" to survive, right? - that would be compatible with a negative(-leaning) view in population ethics according to which what (mainly) matters is the avoidance of unfulfilled preferences).

• It's clear that evolutionary beings will have a massive bias against the idea of childbirth being morally problematic (no matter its merit). Also, people would themselves be suffering/have thwarted preferences from childlessness.

• People consider death an "egoistic" case - a harm to the being that died. I think that's confused. Death is the non-birth of other people/people-moments.

• People usually don't "favor" it in the sense of considering it morally important/urgent/required. They tend to think it's fine if it's an "OK deal" for the being that comes into existence (here again: "ego"-case confounder). By contrast, they think it's morally important/urgent not to bring miserable children into existence. And again, we should abstract from childbirth and genealogical continuation (where massive biases are to be expected). So let's take the more abstract case of Omelas: Would people be willing to create miserable lives in conjunction with a sufficiently great number of intensely pleasurable lives from scratch, e.g. in some remote part of the universe (or in a simulation)? Many would not. With the above confounders ("egoism" and "personal identity", circumstantial suffering, and a preference-based intuitive axiology) removed and the population-ethical question laid bare, many people would not side with you. One might object: Maybe they agree that Omelas is much more intrinsically valuable than non-existence, but they accept deontological side-constraints against actively causing miserable lives, which is why they can't create it. But in that case they shouldn't prevent it if it arose naturally. Here again, though, my experience is that many people would in fact want to prevent abstract Omelas scenarios. Or they're at least uncertain about whether letting even Omelas (!) happen is OK - which implies a negative-leaning population axiology.