I will assume that this is a debate question. For the record, abortion is legal in the United States and in most other developed nations, though we will focus on the United States. The Supreme Court decision Roe v. Wade (1973) made abortion legal throughout the nation. However, subsequent decisions in both Congress and in the Supreme Court have placed more restrictions on access to abortion. For instance, the Hyde Amendment, introduced by Senator Henry Hyde of Illinois, prohibited the use of federal funds for abortions that were not performed strictly to save the life of the mother. Planned Parenthood of Southern Pennsylvania v. Casey (1992) introduced the notion that an anti-abortion law could be struck down if it placed an "undue burden" on one's right to obtain an abortion. In regard to Casey, the Court upheld statutes related to parental notification and a 24-hour waiting period before getting an abortion, but it rejected others, such as spousal notification.
Previously, abortion was legal in some states but not in others, which required women in states who did not provide it to go to neighboring states where the procedure was safe and legal, or even out of the continental United States. Those who could not afford to travel risked their lives with what were called "back alley abortions"—induced miscarriages performed by non-medical professionals. The argument in favor of maintaining Roe v. Wade is that without it, poor women would again resort to illegal methods.
The argument against abortion is that the procedure terminates a life. Advocates on this side of the debate insist that when a woman is carrying another life, she has no right to determine if that life should exist or not, for it is a separate and autonomous being that she has helped to create.
Therefore, in deciding your position in this debate or in how to argue it, it is important to look at the issue of autonomy and whose is most important—the mother or the prospective child. Also, it is important to consider the "right to privacy" protection given in the Fourteenth Amendment (recognized in Griswold v. Connecticut), which was the basis on which Roe v. Wade was decided.