Mackubin Owens makes a distinction that bears emphasizing, quoting McCarthy:

In reality, sharia explicitly invites the presence of non-Muslims provided that they submit to the authority of Islamic rule. Indeed historically, as I related in The Grand Jihad, my book about the Muslim Brotherhood and its Islamist ideology, because sharia calls on these submissive non-Muslims (dhimmis) to pay a poll tax (jizya), their continued presence was of economic importance in lands conquered by Islamic rulers.

It is therefore easy for Islamists and their apologists to knock down their strawman depiction of what a no-go zone is when they leave it at that: a place where non-Muslims are “not allowed.” That is not what no-go zones are—neither as they exist in fact nor as they are contemplated by Sharia. The point of imposing Sharia—the reason it is the necessary precondition for building an Islamic society—is to make Islam the dominant social system, not the exclusive faith. The idea is that once Sharia’s systematic discrimination against non-Muslims is in place, non-Muslims will see the good sense of becoming Muslims. Over time, everyone will convert “without coercion.” The game is to set up an extortionate incentive for conversion while maintaining the smiley-face assurance that no one is being forced to convert at the point of a sword.

So radical Muslims will be welcoming to any ordinary non-Muslims who are willing to defer to their mores. What they are hostile to are officials of the host state: police, firefighters, building inspectors, emergency medical personnel, and anything associated with the armed forces. That is because the presence of those forces symbolizes the authority—the non-submission—of the state.

Notice, however, that no sensible person is saying that state authorities are prohibited from entering no-go zones as a matter of law. The point is that they are severely discouraged from entering as a matter of fact—and the degree of discouragement varies directly with the density of the Muslim population and its radical component. Ditto for non-Muslim lay people: It is not that they are notpermitted to enter these enclaves; it is that they avoid entering because doing so is dangerous if they are flaunting Western modes of dress and conduct.