"The legal basis of this goes back many, many years when U.S. citizens would go and fight for foreign nations that were engaging in combat with the United States," Rogers said. "So what they were saying is, once you've made that choice, you no longer get the protections that you would. I mean, if you join the enemy overseas, you join the enemy overseas. And we're going to fight the enemy overseas."

In his speech at the Wilson Center, Brennan said drone strikes are "ethical" because of "the unprecedented ability of remotely piloted aircraft to precisely target a military objective while minimizing collateral damage; one could argue that never before has there been a weapon that allows us to distinguish more effectively between an al Qaeda terrorist and innocent civilians."

And Obama himself defended it in an appearance last October on "The Daily Show."

"There are times where there are bad folks somewhere on the other side of the world, and you've got to make a call and it's not optimal," he said. "And sometimes you've got to make some tough calls. But you can do so in a way that's consistent with international law and with American law."