Some believe that blurring the boundaries of the two major political parties would be a very good thing as it would make legislative compromise more likely. Historically, it is certainly true that avowedly centrist legislators, such as the Southern congressional Democrats who worked closely with Republican presidents such as Richard Nixon and Ronald Reagan, have played an important role in shaping policy.

There is, however, a significant downside to this blurring of boundaries…

To vote correctly, in the view of Lau and company, is to vote in accordance with your fully informed preferences. And one of the surest ways to increase correct voting is to give voters races in which candidates are reasonably ideologically distinct.

If, like Colin Powell, you strongly believe that we need more regulation of carbon emissions, an approach to deficit reduction that involves substantial increases in federal taxes as well as spending cuts, an immigration policy that gives unauthorized immigrants the opportunity to become lawful permanent residents without first requiring that they return to their country of origin, and an education policy that emphasizes higher levels of public spending over competition among educational providers, it wouldn’t just be unusual to back Mitt Romney over Barack Obama — it would actually be, in the sense articulated by Lau and his co-authors, incorrect.