Most arguments for originalism either claim that judges follow the original meaning of the Constitution because that's what the people "consented" to, or because doing so promotes democracy. Some originalists also claim that their methodology does a better job of constraining judges than do other approaches to constitutional interpretation. Although I am very sympathetic to originalism, I have never found any of these three claims persuasive. Even setting aside the fact that a high proportion of the people at the time did not and/or could not consent to the Constitution back in 1787-88 (women, most blacks, anti-Federalists, etc.), it is hard to see why the consent of long-dead ratifiers 200 years ago should bind us today. Democracy is also a problematic rationale for originalism, since adherence to the original meaning will sometimes require judges to strike down laws that have the support of political majorities. Finally,it may well be true that originalism constrains judges more than many other methodologies do. But if constraint is the main goal (which I don't believe to be true), it would be easy to come up with other decision rules that constrain even more. For example, judges would be most constrained if we, like Britain, simply did away with judicial review altogether.
In recent years, however, originalist scholars have sought to improve on these traditional arguments by trying to show that originalist methods of interpretation lead to better consequences than other methodologies. This short, but important new paper by John McGinnis and Michael Rappaport is a good summary of the emerging consequentialist case for originalism (also available here). Their key argument is that sticking to the original meaning of the Constitution is likely to have beneficial consequences because only that meaning was approved by a broad supermajority process (either the amemdment process or the ratification process of the original Constitution). The fact that the original meaning had to be agreed on by a broad consensus of both political elites and the general public makes it highly likely that it will benefit more people to a greater extent than any interpretive rule that judges are likely to come up with on their own. A rule that has the support of five or more of the nine Supreme Court justices is far less likely to have net beneficial consequences than one that has the support of the vast majority of the population.
McGinnis and Rappaport's case is compelling, but not without some potential weak points. To my mind, the biggest problem may be the fact that the US Constitution is so hard to amend through the formal amendment process that there is a real danger that we could be stuck with an original meaning that, although highly beneficial in its time, is dysfunctional today. A weaker objection is the fact that much of the Constitution was not ratified by as broad a supermajority as the McGinnis-Rappaport theory assumes. For example, as Bruce Ackerman has shown in a series of books, the crucial Reconstruction amendments were only ratified by the necessary three quarters of the states because several southern states were essentially coerced into ratifying by the federal government. For these and other reasons, I am not convinced that originalism should be the sole and exclusive method of constitutional interpretation. However, McGinnis and Rappaport's argument - along with similar ones by other scholars - does persuade me that there should at least be a strong presumption in favor of textualism and originalism that should be overridden only in very exceptional cases.
For those interested in further reading on this subject, I myself have made some arguments that overlap with McGinnis and Rappaport's in this recent critique of Justice Breyer's rejection of originalism. Yale Law Professor Akhil Amar - a prominent liberal originalist - has defended originalism on consequentialist grounds from a left of center perspective, most notably in his article "The Document and the Doctrine," 114 Harvard Law Review 26 (2000) (unfortunately, I don't think that Amar's important article is available on line, but if anyone sends me a link I'll be happy to post it).
UPDATE: Akhil Amar's article is available here.