You write: “Even if you think abortion is murder, there are plenty of open moral considerations that can easily sway you to accept that despite its immorality, its illegality would cause more harm and suffering in the world than at present, and so all else being equal its continued legal status is morally justified.”
This is too fast.
I think what should be said is that if you’re operating within a utilitarian framework the empirical question of whether recriminalizing abortion would lead to more net harm overall is a salient consideration. But if, say, you’re operating under a deontological framework it’s not at all clear, and in fact it’s not very likely, that this consideration should matter.
Under a deontological scheme, murder is overridingly bad, even if outlawing it introduces more harm into the world than allowing it.
But, yes, if utilitarianism seems right to you then this would absolutely be a relevant, and even significant, consideration.