It is not impossible for an act to be both immoral and eligible to the alternative, I would say. In very problematic cases like these, I do think there's a role reserved for the individual conscience.
Let me ask my question in another way. Why do you feel a different legal standard should apply for cases you consider to be "problematic cases"? Isn't it still the case that "very clearly another person being wronged to an incredible degree by it"?
I am firmly on the left and I strongly oppose late-term abortion (without exceptions) though I do not oppose early-term abortion at all.