Just when the West is struggling to make clear to the rest of the world the nature and importance of free speech—and the underlying political separation of sacred and secular—Pope Francis weighs in and muddies the waters. Responding during a flight to the Philippines today to press questions about the Charlie Hebdo killings in Paris last week, the Pope said clearly that “One cannot make war [or] kill in the name of one’s own religion, that is, in the name of God. To kill in the name of God is an aberration.” He said also, however, that free speech does not imply total license to insult or offend another’s faith: “One cannot provoke, one cannot insult other people’s faith, one cannot make fun of faith. Every religion has its dignity.”

So far so good—insofar as his “cannot” implies simply that one “ought not” to make fun of another’s faith, as a matter of good behavior, other things being equal. That caveat is necessary because there are times when religious claims and, especially, practices are rightly ridiculed, as when they threaten to restrict the freedom of those of no or of other faiths. Thus understood, however, the Pope is simply distinguishing between what one has a right to do—speak freely, even if offensively—and what one ought to do—refrain from giving gratuitous offense.

But the Pope did not stop there. He added, “In freedom of expression there are limits, like in regard to my mom”—alluding to an earlier comment, “If [a dear friend] says a swear word against my mother, he’s going to get a punch in the nose. That’s normal.” To be sure, it may be “normal,” but it breaks down the distinction between speech and force—and opens the door to justifying the use of force to punish speech. If legitimate in the personal sphere, why not in the public sphere as well? In fact, American law has such a doctrine, the “fighting words doctrine,” which the Supreme Court held in 1942 in Chaplinsky v. New Hampshire to refer to words that “by their very utterance inflict injury or tend to incite an immediate breach of the peace” and are among the “well-defined and narrowly limited classes of speech the prevention and punishment of [which] … have never been thought to raise any constitutional problem.”

But that doctrine has never sat comfortably within our free speech jurisprudence, and in fact it has been steadily narrowed over the years, for good reason. The proper response to offensive speech is speech in turn. Otherwise, were the force of law to be sanctioned as a proper response, there would be no end to the fine lines that would need to be drawn to distinguish when and when not force would be justified—and no clear bounds on official powers to sanction. Indeed, do we need more than to look around the world to places where speech is not protected? Surely, the Pope did not mean to open the door to blasphemy laws, but he cracked the door just a little.