Separation of church and state in the United States:

The court noted that it "is a matter of history that this very practice of establishing governmentally composed prayers for religious services was one of the reasons which caused many of our early colonists to leave England and seek religious freedom in America." The lone dissenter, Justice Potter Stewart, objected to the court's embrace of the "wall of separation" metaphor: "I think that the Court's task, in this as in all areas of constitutional adjudication, is not responsibly aided by the uncritical invocation of metaphors like the "wall of separation," a phrase nowhere to be found in the Constitution."

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Stewart felt the court was responsibly aided by the uncritical invocation of what?
unanswerable