If you want a reason why an abortion compromise isn't possible, try this contrast: My idea of a plausible middle ground on the issue requires the overturning of Roe v. Wade, followed by a move toward a system in which abortion is legal but discouraged in, say, the first ten weeks of pregnancy, and basically illegal thereafter. Whereas Will Saletan and Freddie De Boer, both serious-minded pro-choicers, are convinced that a plausible middle ground would involve pragmatic pro-lifers throwing their support (and tax dollars) behind America's largest abortion provider, on the grounds that its commitment to preventing unplanned pregnancy makes Planned Parenthood "the most effective pro-life organization in the history of the world."
There are two things to be said about the latter notion, beyond what I said in my last post (and what John Schwenkler has to say here and here and here). The first is that just because it seems intuitive - to liberals, at least - that Planned Parenthood's efforts at making contraception available and affordable dramatically reduce the abortion rate doesn't necessarily make it so. Here I'd refer you to the extended, years-old argument between Megan (then "Jane Galt," of course) and Peter Northrup on contraception and abortion: Suffice it to say that the link between the availability of Planned Parenthood's services and the abortion rate is, well, non-obvious at best. Indeed, a quick gloss on the state-level data from the 1990s that Megan cited in her debate with Northrup would seem to suggest that the best way to reduce your abortion rate is to straightforwardly make abortions harder to get, through legal restrictions and cultural pressure. After all, liberal, well-off, Planned Parenthood-friendly Massachusetts, had a late-'90s abortion rate roughly twice as high as poor, socially-conservative states like Mississippi, Arkansas and Alabama, and more than three times as high as highly pro-life states like South Dakota and Utah.
Now of course correlation isn't causation, and there are presumably many other factors at work in these state-level numbers than just the legal and cultural climate - racial and ethnic disparities, urban and rural differences, and so forth. But at the very least I'd like to see a lot more rigorous, data-rich analysis on this subject before I'd even concede that Planned Parenthood's preventive efforts do have a bigger impact on the abortion rate than legal and cultural efforts to restrict abortion, let alone that they trim the rate of unintended pregnancies sufficiently to outweigh the organization's efforts to make the procedure as cheap and easy to obtain as possible.
But the deeper point is this: The interaction between public policy and social trends is highly complex, and very difficult to predict, and thus there are any number of policy choices that can be plausibly said bear on the abortion rate, for good or ill. The distribution of contraception is just a small part of the pantomime. Which means that once you take the legal debate over the rights of the unborn out of the picture, and start redefining being pro-life as "pursuing lower abortion rates through policy choices," almost any policy preference can be re-cast as "pro-life." Married women tend to have fewer abortions, so clearly ending the marriage penalty was the most pro-life measure of the last fifteen years! But wait: There's evidence that increases in state-level Medicaid funding correlate with lower abortion rates in the short term - so maybe liberal Democrats are real pro-lifers! But wait again: Welfare reform and the economic boom of the 1990s correlated with plunging abortion rates, so maybe free-market conservatives are the real pro-lifers! But wait again: Maybe the abortion rate fell in the 1990s because the sort of women who would have grown up to have abortions were themselves aborted in the post-Roe 1970s ... so people who favor maximizing the abortion rate, paradoxically, turn out to be the real pro-lifers!
You can play this game ad infinitum. If the definition of being pro-life is "desiring the sort of circumstances that tend to reduce the abortion rate," than almost everybody is pro-life, because almost everybody thinks that their favored positions on trade, government spending, tax policy, the minimum wage and so forth will lead to better socioeconomic outcomes overall - and better socioeconomic outcomes overall will probably lead to fewer women seeking abortions. Now I'm obviously happy to have broad debates about public policy, and I certainly think that pro-lifers should be interested in crafting a broadly pro-family politics in addition to seeking a more pro-life legal regime. But the pro-life cause is primarily about issues of law, morality and justice, and if pro-lifers treat the broader pursuit of socioeconomic progress as a substitute for, rather than a complement to, the pursuit of legal protections for the unborn, then they've given up on their movement's raison d'etre to no good effect. Pro-lifers can and should be willing to compromise within the debate about how the law should treat unborn human life, by agreeing to legal regimes that stop short of their ultimate goal. But a "compromise" that involves giving up on that debate entirely in favor of arguments over which domestic-policy interventions will reduce the abortion rate on the demand side is no compromise at all: It would strip the pro-life movement of its purpose, drain it of its idealism, and transform it into an advocacy group for, well, good public policy, which practically every other political movement and organization claims to be already.