As noted by the Washington Times, this was Roberts' response to questions regarding the use of foreign law as precedent:
Judge Roberts also indicated he would firmly oppose the movement - aggressively supported by several current justices - to look to foreign law as a guide to interpreting our own Constitution. This use of foreign law, Judge Roberts pointed out, "allows the judge to incorporate his or her own personal preferences, cloak them with the authority of precedent - because they're finding precedent in foreign law - and use that to determine the meaning of the Constitution."
I think this is a hard argument to rebut. There is ample evidence that when given the opportunity to support an otherwise flimsy argument that judges will use any device available to them to prop that argument up. Legislative history has been a battle ground in this sense for quite a long time, but it now seems that the use of foreign law precedent is the wave of the future.