Obama has been taking a lot of heat for saying that as president, he would take military action against high-level Al Qaeda forces in Pakistan without that government's permission if the Pakistanis failed to act themselves. There's a certain level of irony in that the critics mostly decry Obama's failure to be vague about this, rather than his actual policy, and then they use the fact that he was vague on just what military action he would do to claim he's talking about a full-scale invasion, like the one that the neocons wanted/still want to do with Iran.
Obama isn't an idiot like the neocons; he's talking about covert ops or small-scale military ops (missiles and in-and-out raids). From my perspective, this is fine ethically, as long as we accept the Golden Rule. Here's the hypothetical: suppose Pakistan locates high-value terrorist leaders targeting Pakistan for something terrible, at a location in the United States, and the US refuses to act against them for whatever reason (maybe the Pakistanis trust their intelligence sources while the US doesn't). Pakistan has the same right to move against these people as we have against Al Qaeda in Waziristan. I don't see any part of this hypothetical as being completely impossible, by the way, including Pakistan's ability to act. They can't launch cruise missiles, but they can send some spies with easily-purchased-in-America, modified automatic weapons to shoot up a terrorist meeting, probably with less collateral damage than a cruise missile would bring.
So I don't see a way around this ethically,* although I would love to witness the contortions of American Exceptionalists in order to claim our moral leadership allows us to act in self-defense in ways that are denied to other nations.
Now, ethics is only the first test; the second test is whether it's a beneficial policy to actually follow, and the third test is whether it's beneficial to openly talk about this policy. I don't really have an answer to the second test because I don't know when the benefit of taking out a particular target exceeds the cost to Pakistan's fragile political structure (assuming the action becomes known). I think it would, if it were 100% certain that cruise missile strikes would kill Osama and Zawahiri with 0% chance of collateral casualties, but beyond that scenario, you have to be more of a Pakistan expert than me.
As for the third question of whether one should talk about this policy, I also think that's okay if you acknowledge the Golden Rule. Obama's statements have already caused unrest in Pakistan, but I think some of the edge could be taken off by acknowledging that the shoe could be on the other foot. Obama could quickly add that in fact, covert foreign action in the US would be unnecessary because the US will act against terrorism plotters, and so any such attempt would be wrong and have negative consequences.
Whether any American politician would acknowledge this Golden Rule application, though, is an open question.
*The one potential way around is to say neither we nor the Pakistanis can act ethically in this manner and must use the legal process instead, but that's an outlier position in today's world.