Writing in The Atlantic, Matthew Yglesias does a good job emphasizing a point I've also made here -- namely, that the reduced partisanship of the mid-twentieth century was largely a result of the ugly history of race in the South:
Yet as today’s presidential candidates call for a less divisive kind of politics, it’s worth recalling the 1950s. While polarization has its drawbacks, the alternative is often worse.
The mid-20th century is sometimes remembered as an era of cozy political consensus, but in fact the corridors of power echoed then with starkly disparate voices... The politics were no less contentious than they are today. They were just less coherent.
The looser partisanship of the period was mostly the result of racism and its complex role in the politics of the time. The legacy of the Civil War had made the Democrats the party of southern white supremacists, but the legacy of the New Deal had also made them the party of northern liberals and many urban African Americans. These latter constituencies were demanding federal intervention in southern affairs to secure the rights of southern blacks. At the same time, many members of the GOP—the traditional home of black voters and the party of racial progress in many states—were resisting these demands, which struck them as violating the principle of a modest federal government.
The result was a muddle.
Indeed, as I've shown, the period was a historical aberration. Once the parties realigned on race and conservative Democrats left the party, the political system returned to its historical norm of partisanship and polarization.
There are certainly many negative aspects of this change, but as Yglesias rightly notes, it does reduce the complexity of the choices facing voters:
But for voters, the boring new ways can be looked at in another way—they’re straightforward. Elections have a predictable and easy-to-understand relationship to government action. Electing a Democrat means, on the margin, more spending on the federal safety net and more government regulation, while electing a Republican produces policies more favorable to business interests.
Journalists who lament the glorious bipartisanship of the 1960s and 1970s would do well to remember these two points.