A fetus may be a human being, but it’s not really a person.
Sometimes, supporters of legal abortion will concede that an embryo or a fetus is, scientifically speaking, a human being, while denying that it is a person with rights. However, when pressed, they can point to no meaningful distinction between human beings and human persons. “Personhood” is a philosophical term, not a scientific one, and
ultimately depends on individual, subjective beliefs rather than common, objective values.
Moreover, history is replete with attempts to exclude certain categories of human beings from the class of “persons” enjoying human rights, in an attempt to rationalize such injustices as slavery or genocide. Human rights are meaningless unless they belong to all human beings, without discrimination.