Yesterday’s Washington Post reported that Senator Barack Obama claims he can move the country out of “ideological gridlock” and bring the country together more effectively than can Senator Hillary Clinton. This declaration is consistent with Obama’s broader claim, which is that he will put an end to “polarizing politics.”

Obama is attempting to tap into something real, which is the reluctance on the part of many Americans to be drawn back into the psychodramas of the Clinton years: Ken Starr and Kathleen Willey; private investigators hired to look into the private lives of women alleged to have had affairs with Bill Clinton; the (still-resonating) charge of a “vast right-wing conspiracy”; and the brass-knuckle tactics of James Carville, Paul Begala, Sidney Blumenthal, and others. Most of us would like that chapter of American politics to stay closed.

At the same time, the claim that a divided America is somehow “bad” is itself intellectually sloppy. Most of us prefer social harmony to discord—but unity is not the only, or even the highest good in politics. Was there a more divisive and reviled president than Lincoln, who uprooted the centuries-old institution of slavery? The biographer Robert Jackson wrote that after Franklin Roosevelt had been in office for a brief period, “the lines began to separate between those in whom he inspired an all-out devotion and those in whom he aroused an implacable hatred.” Martin Luther King, Jr. was “the object of bitter hatred.” And in 1984 the pollster Lou Harris claimed that Ronald Reagan was polarizing the country more than any president since FDR.

“Conviction politicians” are often polarizing because they take ideas seriously and are willing to do battle on their behalf. And often the greatest advances in history come about only after contentious political debates led by brave and, yes, polarizing political leaders.