This will, to say the least, be alien to your customary ways of thinking, but the relationship between the people and the sovereign is a relationship of love. You may forgive failures on the part of someone you love a thousand times before you finally call it quits. Pakistan has seemed at or near that point many times. Its lack of self-respect is directly related to its lack of respect for others. A better sovereign would not host international terrorists, and would not put others in the position of having to set aside its weakened sovereignty claims. Before you accuse the US of hypocrisy, respect for the "privacy" of others stops at the point of reasonable self-defense or intolerable violations. Disarming a thug doesn't make you a hypocrite about the right to bear arms. You don't normally interfere with someone else's parenting methods, but protesting child abuse or even calling up social services or the cops on an abuser doesn't make you a bad parent or a hypocrite.

Mr B-P, Daesh demanded that the US and allies stay out of Iraq or face further Daeshian wrath as exemplified in the gruesome killing of the captives. The executioner cited particular actions - contemporaneous bombings - but his organization's disagreements with America and America's allies are boundless. The demands were apparent, and aggravate the act, but even without them, even without the war-pornographic video, the special interest of the US in the lives and deaths of its own citizens is basic: It's embedded in the very definition of "nation."

Yes, it goes without saying that Pakistan will be concerned both about its own citizens and its own soil. That also means that if Pakistan chooses to look the other way in particular instances, that's also Pakistan's right. Countries frequently choose to look away when presented with potential causes of war, or, more typically, to satisfy their injured honor or interests by other means. A state that does not respond adequately or at all to such challenges tends to put its own right and ability to govern in jeopardy.

If the murderers were officials empowered to speak on behalf of the US government, and promised to kill more Pakistanis unless Pakistan acceded to US demands, then Pakistan would have cause. Even if the killers were stray individuals merely claiming to act and speak for the US, but the US refused to arrest them or pursue the case, Pakistan would have the right and responsibility to act on its own to the extent it could, including by acts that under a strict definition might qualify as acts of war - as the US omissions might be adduced in a case for war. Even if the murderers were unknown or completely unattached to the US government, Pakistan would have a special interest in the case, which in the realer world would be acknowledged by the USG. I think the pattern is that a responsible government will prosecute murders of foreign nationals on its own soil, but that foreign governments sometimes seek extradition or the right to prosecute according to their own laws as well, depending on specific details of the case and trial, treaty obligations, and other factors.

Being American was the particular crime or sin of which Daesh found those journalists guilty, and that makes their murders of special interest to all Americans, and legitimates action against Daesh as national self-defense, even before we get to all of the other things Daesh has done that we have long insisted are unacceptable and inherently threatening to our "existence."