Should abortion be defended as a "Good Thing", or a necessary evil?

Nathan Newman blogs that abortion should be defended as a "good thing", and that Howard Dean's statement to the contrary is "asisine":

If abortion is never a good thing, then why should anyone have the option to have one?"

One reason progressives are not as strong on the abortion issue is that we so rarely hear abortion defended on its merits. Instead, we have the religious right denouncing it as the equivalent of murder and slavery, and progressives essentially saying "that may be, but it's really none of your business if people are committing murder and slavery, now is it?" (Nathan
Newman)

Why should anyone have the option to have one? What kind of fascistic state does Nathan Newman thing we live in? McDonald's cheeseburgers are never a good thing healthwise, but that doesn't mean people shouldn't have a right to eat them.

Nathan also says pro-choice people should trumpet Steven Levitt's argument in Freakonomics that the legalization of abortion in the 70's is correlated to the drop in crime in the 90's (less unwanted babies means less robbers 20 years later).

Steven Levitt makes a good case for this correlation, but even he admits it's an awful way to defend abortion:

Levitt: I have gotten a whole lot of hate mail on the abortion issue (as much from the left as from the right, amazingly). What I try to tell anyone who will listen -- few people will listen when the subject is abortion -- is that our findings on abortion and crime have almost nothing to say about public policy on abortion. If abortion is murder as pro-life advocates say, then a few thousand less homicides is nothing compared to abortion itself. If a woman's right to choose is sacrosanct, then utilitarian arguments are inconsequential. Mainly, I think the results on abortion imply that we should do the best we can to try to make sure kids who are born are wanted and loved. And it turns out that is something just about everyone can agree on. (Steven Levitt, interviewed on kottke.org)

Abortion is either killing, or it's not killing. If it is killing, than our government would effectively be condemning people to death for "pre-crimes" by using lower crime statistics as a justification for pro-abortion policy. If it's not killing, then the policy shouldn't require this sort of Benthamesque calculus, and by going to the extents of applying it, the pro-choice crowd will actually seem to many to be conceding that it is killing.

Arguments for abortion must remain libertarian if they are to have any hope winning over support among the right, because the right exists as a not-so-delicate balance between religious moralism and libertarianism. They have little appeal for the "great society" championed by the democrats of old. Pro-choicers should reserve this argument strictly to liberals or socialist who, like some of the Christian Right, see the state as a better arbiter of good and bad than the individual.

Newman's argument is also a slippery slope towards forced abortion and/or sterilization, which was briefly experimented with in India under Indira Gandhi, with horrendous results. If abortion is a good thing sometimes, why not force it on pregnant poor people who don't seem like they'll be able to take care of their potential child? This would be the logical conclusion of a policy that gives greater value to the "social good" argument than the women's rights argument.