The debate over whether it counts as "human" is, at best, a distraction. Like with literally any other circumstance where one person's right to life rubs up against another person's bodily autonomy, bodily autonomy should win. The alternative means you support forcing people to donate organs/tissue against their will, to save another's life. That's the simple and obvious example where these two conflict, outside of the abortion debate, and nobody is arguing for forced organ donations from living persons. Everyone sees that for the horror that it would be.
And denying women abortion rights is exactly the same horror. It's the same violation of her rights, for the same reasons. It isn't a magically more-convincing argument when it's about a fetus rather than a living person. Even if we allow the fetus to be considered a person, that just puts pro-life on the same level as forcibly harvesting organs/tissue from the unwilling. Even if we just stick with that which can be regrown in time, like portions of your liver and various tissues, as opposed to whole organs like kidneys. That's the best-case scenario for the pro-life argument.
And the reality is that when we add that there's a lot of reasons to not consider the unborn fetus a human being, it gets even more objectionable to deny abortion rights.
We don't allow for forcing someone's body to be seized to support another's life in any other circumstance. Why should we do so in the case of pregnancy? What possibly justification could you come up with for a special treatment of these rights in that particular instance? Whether the fetus is a human being or not isn't relevant, because even if we allow it, there's still no justification for this kind of horror show. Any more than there would be forcibly harvesting part of someone's liver, or skin for a skin graft.
I don't see the "intractably difficult" part of this. I see emotional appeals of "but it's a BABY" that ignore that under no circumstances, for any other person, would we ever consider this kind of abuse of human rights.