Who or what is using the uterus without the woman's consent?
In the case of a woman wanting an abortion, the fetus inside of the uterus.
Side question, do you think a fetus is a human being, regardless of legality or policy? When do you personally believe life, human life with rights and worth protecting, begins? Again, without commenting in this context on the women's rights, since it is entirely possible to believe that life begins at conception but that a right to an abortion outweighs that belief.
Human life (as separated from other types of ape life) began a few million years ago, and has been passed along continuously. The sperm and the egg were alive before conception. I think the zygote has rights at the moment of conception, but not rights that supersede the rights of the woman in whom the zygote is created (assuming the zygote is created there), just like any other person.