The US is using the drones in the context of the so called 'war on terror' to change international law. Over the last 150 years, U.S. citizens have written much of the international law that is out there, yet the U.S. generally exempts itself from those laws. Even so, this is a new trick, where by it is noted that the "Common Law" is defined by precedent (you can find this in ICRC documents on international law) and so, the U.S. now contends that if the most powerful nation in the world sets a new precedent, then so be it - that becomes the law.
The use of drones is particularly disturbing because they spy and use lethal force outside of designated war zones. This undermines those boundaries. I used this point in my testimony at one of the trials where I was a defendant. The Hague Conventions of the late 18th and early 19th centuries specifically say that if you have a weapon whose capabilities don't fall under current international law, you can only use it in ways that abide by current law until the international community can come together and decide how it should be used. These days, the U.N. addresses these issues after the fact and the U.S. ignores the resultant treaties.