I completely agree with Silvana that Kagan's credentials as a consensus-builder don't in themselves undermine her liberal credentials. On the other hand, as I implied yesterday, I don't think that one should be under any illusions that Kagan actually will be able to build consensus on the Supreme Court as she did in her admirable tenure as an academic administrator.
It's worth remembering that while Roberts established the goal of getting much more consensus on the Court, he's utterly failed to actually achieve this goal. And if Roberts can't do it as a chief justice from a majority position, Kagan certainly won't be able to. This isn't a criticism of either justice -- it's just that, as Silvana later says, there are many issues the Court faces that aren't amendable to substantive compromise.
I also want to look at Silvana's argument that unanimity "increases the Court's legitimacy and improves public confidence in the Court's decisions." While this seems intuitively right, it's actually very difficult to demonstrate that this is true. The perception of increased polarization hasn't actually led to a decrease in the Court's legitimacy.
I'd also point out that while some of the Court's most controversial decisions were 5-4, many were not. Brown, which generated an immense backlash, was unanimous. The school-prayer case Engel v. Vitale, which generated the most hate mail of any case in the Court's history, had one dissent. Roe was 7-2. On the other hand, Bush v. Gore -- a 5-4 decision, that had an unusually high level of public visibility, with a majority opinion that was not exactly a model of legal craftsmanship -- has had no discernible net effect on the Court's public legitimacy as outrageous as it might have been.
Without claiming that it's a good thing, I think the evidence is pretty compelling that the legitimacy of the Court is determined by results, not by the reasoning used by the Court or by how many people sign on to a Court's majority opinions.