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Anti-slavery crusader William Wilberforce certainly deserves a film, and if Amazing Grace isn’t equal to his achievements, it’s a useful introduction to them. The film’s release is keyed to the bicentennial of Britain’s anti-slave-trade act, which was passed on March 25, 1807. But it opens years before that, when Wilberforce (Welsh hunk Ioan Gruffudd) spies two men beating a horse. The scene illustrates Wilberforce’s empathy—he was among the co-founders of the Royal Society for the Prevention of Cruelty to Animals—but also functions as a metaphor: The beaten horse embodies the abused slaves the movie largely keeps off-screen.

Films in which white crusaders battle for barely glimpsed blacks are often condemned, but in this case the setup is historically accurate. Wilberforce was elected to the House of Commons in 1780, when he was 21, and battled to abolish slavery until he retired in 1825. (He died in 1833, the year slavery was finally banned in British territories.) Although slave ships docked in British ports, most of the men and women they carried to bondage were held in the colonies, chiefly Jamaica. So it’s entirely reasonable that the movie’s only African-born character with a speaking part is Olaudah Equiano, a freed slave whose memoir became a London bestseller. (The part is played by Senegalese master musician Youssou N’Dour, whose presence is more a nice gesture than ideal casting.)

Equiano is a member of an anti-slavery committee, mostly comprised of Quakers, that advises and sometimes goads Wilberforce; chief among its members is Thomas Clarkson (Rufus Sewell), a hard-drinking firebrand. Wilberforce also seeks counsel from John Newton (Albert Finney), a former slave-ship captain who became a pastor and passionate slavery foe, and who wrote the lyrics to the song that provides Amazing Grace with its title. In Parliament, Wilberforce’s allies include William Pitt the Younger (Benedict Cumberbatch) and, ultimately, Lord Charles Fox (Michael Gambon), who changes sides midway through the struggle. Allied against him are the wily Lord Tarleton (Ciarán Hinds) and the imperious but ineffectual Duke of Clarence (Toby Jones). Whenever these men puckishly debate, the resulting electricity is a testament to the British period-piece acting tradition.

To keep the story from too closely resembling an illustrated lecture, director Michael Apted moves back and forward in time, sometimes showing Wilberforce as young and vigorous but also depicting his midlife crisis, caused by a ferment of legislative failure, chronic colitis, and the laudanum he took to ease the disease’s pain. Scripter Steven Knight, who wrote the much grimmer (and even more melodramatic) Dirty Pretty Things, also inserts Wilberforce’s whirlwind romance and contented marriage with Barbara Spooner (Romola Garai), a plot strand that seems both underdeveloped and too prominent.

This is a story that can be used for many purposes, and Apted—a skilled if styleless technician whose credits range from a James Bond flick to the 7 Up documentary series—seems to want to further all of them. When Wilberforce denounces the British war against the American former colonies, the Iraq parallels couldn’t be more obvious. Yet Amazing Grace also bolsters Christian zealots who see their religion as the source of most, if not all, moral improvement in human history. (The movie was financed by Bristol Bay Productions, which is owned by aspiring media magnate and right-wing Christian activist Philip F. Anschutz.) Although Wilberforce has his dark moments of doubt, he (and the Quakers, of course) regularly invoke their religion. But then that, too, is historically justified.

Indeed, most things in the movie can be justified, although not the closing scene in which Wilberforce is applauded for his anti-slavery campaign, or the way David Arnold’s treacly score swells every time someone says something that’s supposed to be moving. Apted doesn’t trust the viewer to discern anything, even that Wilberforce is the movie’s hero—a fact established in the very first scene. There are a dozen ways that this film could be subtler, but then political campaigns tend to be overstated. Even though it’s fighting for a cause that’s already won, Amazing Grace doesn’t leave any room for doubt. It would rather be right than artful.