There are more simple, and simplistic, arguments against abortion and less simple and simplistic arguments against abortion that all appeal to the idea of fetuses being human. Here are some arguments, too briefly stated and not at all explained, ordered from more simple to less simple:
Abortion is wrong because:
- Fetuses are biologically human.
- Each fetus is a human; fetuses are humans.
- Fetuses are biologically human beings.
- Fetuses are biologically human organisms.
- Fetuses are a "kind" of being that's a rational being: fetuses' "essence" is that of a rational being.
Reply to Christopher Tollefsen on Abortion, in Bob Fischer, ed., Ethics, Left and Right: The Moral Issues That Divide Us (Oxford University Press, 2019).
your "essence" is that of a free and rational being; that essence *makes* it wrong to kill you; you have always existed whenever your body existed; your body began at conception; and so you existed at conception and were wrong to kill; and the same is true for all other human fetuses.This argument is discussed here.