Then viability seems an eminently reasonable threshold. If you’re agnostic, there’s no intrinsic value to a clump of cells. If the fetus is capable of surviving on its own but can’t by virtue of being stuck in place it deserves protection.

Of course, when it’s threatening the life of the mother then even though there’s no malice or intent, it is legally justifiable to treat it as we would anyone else who would threaten a woman’s life.