In his recent Green Bag article, discussed in Orin Kerr's post, Prof. David Garrow, one of the country's top Supreme Court scholars, laments the fact Supreme Court clerks increasing come from court of appeals clerkships with "exceptionally liberal or highly conservative" 'feeder' judges, rather than with "equally well-respected but ideologically moderate jurists."
The implication is that "ideologically moderate" clerks and justice are for some reason preferable to those who are "exceptionally liberal or highly conservative." Contra Garrow, I don't see any reason to believe this to be true.
One possible reason to prefer moderate clerks and judges is that they are more likely to reach correct decisions. This, however, is definitely not Garrow's argument. After all, Garrow's own views on the substantive constitutional law are far from being moderate, as one can see in his scholarly work on substantive legal doctrine; see, for example, his well-known book on judicial protection of abortion and sexual freedom. This is not a criticism of Garrow (my own views are no more moderate than his are), but it does close off the most obvious possible reason for favoring centrist judges and clerks. Indeed, Garrow's preference for centrist clerks seems, ironically, to be a preference against clerks who share his own strongly liberal political and legal views!
Instead of relying on the supposed correctness of their views, Garrow's preference for centrist clerks seems to be based on a belief that ideologically more extreme clerks (and possibly judges as well) are more likely to allow "disreputably partisan" considerations to influence their decisionmaking. If I interpret his argument correctly, Garrow is suggesting that committed liberals and conservatives are more likely to allow their policy views to influence their interpretation of the law than centrists.
I see little reason to believe this. Garrow's analysis implicitly conflates having moderate views with not having any ideological commitments at all. In reality, however, moderates do have political views and partisan loyalties, and these views and loyalties may be just as strongly held as those of liberals, conservatives, and libertarians. In cases where the strict adherence to the law leads to ideologically extreme results, moderates may well be tempted to follow their policy preferences instead of the law - just as conservatives and liberals might in cases where the law leads to results they dislike.
Indeed, in two important ways moderate jurists may be more prone to ideological judging than more extreme ones. First, moderate judges such as Justices O'Connor and Kennedy, are more likely to favor complex balancing tests than strong liberals and conservatives, who are more likely to favor bright line rules. Balancing tests tend to leave more scope for judicial discretion (and thus ideological decisionmaking) than rules do.
Second, I suspect that moderates are less likely than comparative extremists to realize that their political preferences are the products of a contestable ideology rather than of simple, nonideological "common sense." Indeed, Garrow's own article partially endorses this fallacy, to the extent that he assumes that moderate views are, by nature, less "ideological" than extreme ones. Of course, if you believe that your views are just common-sense truths that only extremist wingnuts/moonbats could disagree with, you are less likely to be hesitant about imposing them on others through the use of judicial power.