Supremes Cite European Opinion on Death Penalty

From Powerline:

Justice Kennedy relied on international law and practice to "confirm" his view that the juvenile death penalty constitutes cruel and unusual punishment. He also cited the International Covenant on Civil and Political Rights, which the U.S. signed only subject to the reservation of its right to impose the death penalty for crimes committed by persons below eighteen years of age.
In my view, the reliance of foreign law and practice is a symptom of the Court's problem, not the problem itself. The Court has appropriated from the American people the role of social arbiter. Thus, it strikes down longstanding policies and practices adopted through the democratic process on the grounds that five or more Justices personally don't approve. This creates a question of legitimacy which causes the Justices to scrounge for support. Since the Justices preferences often don't correspond to the preferences of majorities here, they naturally look to Europe. They lack the political savvy to realize that doing so only makes their work seem even less legitimate.

Or perhaps I'm completely wrong. Maybe the offending Justices don't really care about whether the Court is perceived as legitimate, and just refer to international stuff because they are trained to cite things.