Note: I haven’t really thought that much about abortion, so I’m sure most of what I say has been covered elsewhere or is for one reason or another foolish. But at least by writing my thoughts down, someone will (hopefully) tell me the reasons that what I’m saying is foolish.
A consequentialist can come to very different conclusions about abortion depending on their theory of the good/bad. If one is a anti-frustrationist (as described by Fehige in "A Pareto Principle for Possible People"), the bad is frustrated preferences. Unborn children don't have preferences at all, so not conceiving them is fine. But a 10 year old probably has a preference for life, killing them would frustrate that preference which is what grounds its dis-value according to anti-frustrationist consequentalism. Abortion, as the midpoint between killing kids and contraception, is notably murkier. When does a fetus gain a strong enough preference for life that killing them would be bad enough that we should generally assume it would be wrong to do so? I'm not sure and am pulled in different directions here.
Beyond that, if one is a longtermist, I think the instrumental considerations outweigh direct ones here. Sure, on the hedonistic total utilitarian (HTU) conception more children living happy lifes is good (AMF, pro-natalism, ...), but if we think that a particular child could develop great anti-extinction tech or marginally increase extinction risk then this plausibly outweighs the direct happiness they experience in HTU's eyes.
I think you completely miss the point about abortion. Women, like other living being, are free to dispose of their own bodies. Whenever we agree or not, women will keep aborting. The utility to provide safe methods is a mather of public health. That's all there is to it.
I think people should have as many kids as they can comfortably care for (physically, emotionally, financially) without being a burden on others.
That will differ from person to person, but at a societal level something about women wanting 2.5 kids on average and ending up with 1.5 kids on average seems wrong. Don't even get me started on the TFR black hole that is East Asia.
I don't have a problem with abortion if its in service to this goal. A family that aborted a Downs Syndrome kid would be fine with me, especially if it was an attempt to increase their family size and doing so allowed them to better care for their remaining kids (and perhaps have more).
The kind of abortion that freaks me out is the kind were you are fucking around with the wrong sort of partners and basically using it as a form of birth control. A lot of women do this, I've seen it, and it's basically what people really dislike when they dislike abortion.
This just seems like a reductio of utilitarianism to me, FWIW.
Motivated reasoning is definitely a thing.
I'd say we evolved to find stuff like this abhorrent because it helps us keep the next generation going and leave it at that.