Unwind by Neal Shusterman is the first novel in a series of dystopian YA where a second civil war was fought in the US over abortion. Shusterman built a fairly complex world for this series, so there's a lot that you can do with an argumentative essay. The first novel was written in 2007, so you can argue how the themes of the book have interacted with real life policy and debates over the last decade show the importance of the novel. Looking at actual policy, you could argue whether or not the policies in the book are realistic, given our own political climate. Along with that, there's a fair amount of "controversial" decisions reached in the novel—tithes and storked babies, for instance. Looking at these, you could argue that the novel either helps or hurts abortion debates. For example, arguing that the idea of parents willingly giving a child to be unwound as part of a religious dedication is so horrifying to readers that it helps pro- abortion arguments that try to take religious extremism out of abortion debates.

One way that I think that you could go with an argumentative essay is to talk about the pro-life and pro-choice debate.  The entire reason that the people in the book allow unwinding in the first place is because they felt it is a nice middle ground between allowing abortion or outlawing abortion.  A parent must give birth to the child, which satisfied the pro-life camp.  But between a certain age range, the parents could retroactively abort the child through the unwinding process.  That arrangement satisfied the pro-choice camp.  People didn't think of unwinding as murder, because 100% of the unwound individual would be harvested for organ and tissue donation.  You could could write your argumentative essay in favor of pro-life, pro-choice, pro-unwinding, or anti-unwinding.  

You could also write the argumentative paper about the author.  You might write your essay that argues Shusterman is pro-organ donation or anti-organ donation.