If a five-day-old blastocyst carries the same moral weight as a born child, why does the law, medicine, and common moral intuition treat them so differently in nearly every other context?
That gap is the whole debate. The FOR side has to establish that a fetus is a person from conception, and that's a contested metaphysical claim, not a settled fact. You can't build a moral prohibition on a premise reasonable people reject.
And even if you grant the fetus some moral status, that doesn't settle it. Nobody is morally required to lend their body to keep someone else alive, not even after birth. Imagine a stranger who needs your kidney, your blood, months of your physical endurance. We don't compel that, and we shouldn't.
So absent overriding reasons, I don't see the immorality. I see a contested claim being asked to do too much work.