Ethicists tend to view issues such as abortion through a utilitarian lens strictly, which has always struck me as odd since there is no reason to suppose a priori that any monoaxiomatic moral system is true. Most people do not seem to need their morality to be governed by a single all-encompassing axiom such as maximising utility; it is just something fetishised among academics.
Utilitarian myopia leads to rather odd things, such as endorsing post-birth abortion on the grounds that the child does not have knowledge of the future, does not experience pain when it is killed, is unwanted, will have bad experiences in the future, etc. Some revealing counterexamples:
Suppose you know a 115-year-old. She and her family are expecting her to be dead imminently anyway, she has already had all the “experiences,” good and ill, that one could reasonably expect a human being to have, and you can kill her in her sleep in some untraceable way, painless, and her loved ones will be none the wiser as to its being anything other than a natural death. There is extraordinarily little, if any, utility lost in this situation. Some, including me, would argue that it is less morally wrong than killing someone who does not satisfy some or all of these criteria. However, I’ll bet most people would be very hard-pressed to say that it is straightforwardly okay.
Utilitarians are often vegans, too. On that note: male chickens tend to be killed as soon as they hatch – they are not useful. Multiple killing methods exist, but one of them involves the use of inert gas; they go through a machine, inhale it, and die immediately. Again, it is hard to pinpoint the loss of utility in this, yet I would guess that utilitarian vegans would be loath to accept that the industrial-scale genocide of male chicks every day is morally acceptable, regardless of how or under what circumstances they are killed.
TL;DR: life itself is valuable; at least, life above some threshold of development is. Thus, pro-lifers are correct when they argue that, at the very least, some humans have a (forfeitable) right to life which does not depend on utilitarian considerations. It is much easier to accept this than to tie oneself in knots trying to refute post-birth abortion proposals with felicific calculus.
In light of that, where is the line to be drawn? Is a foetus at 12 weeks as “developed” or as conscious as those hatchlings? I suspect not. 20+ weeks? It isn’t as clear at that point. So, erring on the side of caution, 12 weeks does not sound like a bad standard, especially since the overwhelming majority of abortions happen before then anyway, so eugenic abortion is still actionable within this framework for the 90% of abortions that occur within that window.
And if you extend this principle to the rest of animate life, you see human hunters of predatory animals in a different way. I do not mourn the loss of wolves, lynxes, and brown bears in Britain, for the aforestated reasons and the obvious one: the insane amount of suffering that goes on in the living world, caused by predators mostly, which tends to be romanticised in the most grotesque way by wildlife documentaries. And the herbivores? In theory, one could leave them alone, create artificial habitats for them, or perhaps even sterilise them before their environments are inevitably destroyed by human exploitation for food and resources, but I see no prospect of this when human governments are unable to co-operate on the most basic of things let alone something so expensive and complex – and you can forget it if the future belongs to the Chinese.