It is now common to view Roe v. Wade as a low point in the history of the Supreme Court -- a conceptual failure one or two notches above Plessy v. Ferguson perhaps, but embarrassing nonetheless. Even a stalwart supporter of women's rights such as Justice Ruth Bader Ginsburg has said the decision moved "too far, too fast," embracing a new right to abortion before the American public was ready for it.

Warnings about Roe have pervaded the debate over same-sex marriage. Should the court be wary of inflaming opponents by recognizing -- prematurely -- the right of gays to marry? Or, as the New York Times put it this week, citing a compelling Yale Law Review article, do the Ruth Bader Ginsburgs of the world "misread the legal and political landscape at the time of the Roe decision," which was already contentious?

On legal grounds, Roe is easily derided. There is no mention of abortion in the constitution and the ruling's claim to authority rooted in a constitutional "penumbra" sounds absurd, a desperate assertion of legitimacy to paper over the constitutional equivalent of a virgin birth.

Yet as a political achievement, the decision, written by Justice Harry Blackmun, succeeded in striking an extraordinary balance that, four decades later, endures.

It's hard to imagine how any ruling could better capture the ambiguities and conflicts with which Americans approach the issue of abortion. With the exception of a brief and modest dip in the early 1990s, a stable, if slim, majority of Americans has long supported the view that abortion should be legal only under "certain circumstances."

The parameters are hazy, but most Americans want abortion to be legal, accessible and discouraged. Their hedged discomfort is embodied by Roe, which is perched between unfettered abortion rights on one side and strict prohibition on the other. The division of pregnancy into pre-viable and post-viable phases has essentially governed abortion policy ever since the ruling was handed down.

In fact, far from undermining political consensus on abortion -- evidence for which is scant -- Roe may have helped create the muddled consensus that has kept an essentially insoluble conflict from spiraling out of control. In 2009, according to the Centers for Disease Control, 64 percent of abortions were performed at less than eight weeks' gestation and 91.7 percent were performed at less than 13 weeks. Only 1.3 percent were performed after 21 weeks.

In effect, the practice of abortion in the U.S. largely conforms to Roe's viability guidelines. It's hard to imagine a ruling more Solomonic or sturdy given the wholly incompatible demands from abortion combatants. There simply is no way to rectify total freedom for women to control their bodies on one hand with total protection for a fetus in the womb on the other.

Yet for 40 years, extremism has mostly been kept at bay despite the view of a vocal minority that abortion equals murder. And a qualified right to abortion, remarkably in sync with both public opinion and medical practice, has been sustained by Roe.

I leave it to others to decide whether Harry Blackmun was a poor constitutionalist. But based on what he achieved with Roe, he was surely a brilliant politician.

(Francis Wilkinson is a member of the Bloomberg View editorial board. Follow him on Twitter.)