Only by wrenching logic and science all out of shape can you claim that a fetus is a human being. Given the right conditions it will indeed develop into a human being but at the age that most fetuses are aborted it has no ability to carry on any of the functions we see as human...it is are not capable of thought, does not even have the neural/neurological equipment to perceive outside stimulus. The main argument against a state abortion ban is practical and humane however.

Regard abortion as a Pandora curse if you want, it's out of the box and no amount of legislation will stuff it back in. When a woman discovers that her pregnancy is doomed by defects, when it threatens her health or future fertility, when it disrupts her educational or professional future, when she has existing family obligations that suffer if she carries another pregnancy to term, when she is too young, or has been sexually abused or raped or is under the threat of abusive parent or partner, she's often going to seek an abortion and the only thing the state can "accomplish" is to make that abortion dangerous (abortion is far safer than carrying to term) or fatal.