The U.S. preferences are always to capture the terrorists because of the intelligence that can be gathered, but lots of the terrorist networks operate in a very remote regions and it's very difficult to capture them. However, of what we can discern from the pattern of drone strikes is that essentially Pakistan's been declared a no-capture zone. Captures automatically are not considered feasible.
If you just look at the numbers, there have been dramatically more people killed in recent years than captured. Three to four thousand people have been killed in targeted killings and only a handful have been captured. Despite all technological and human assets there's a lot of room for error. In drone attacks alone, over 300 children were killed. Those murders have to call into question the credibility of the kill-list methodology, because vast majority of strikes in Pakistan are against people whose identities the Government doesn't know.
Under the interpretations from the administration and the members of Congress, drone strikes could go on indefinitely against enemies who keep morphing into new enemies, but killing should be the exception not the rule. The U.S. should not have been using military force to attack innocent civilians let alone children. What kind of policy says it is legitimate and even sensible to assassinate a 16-year-old boy?
Before any strike is taken there must be near certainty that no civilians will be killed or injured. That is not the case with the so called "signature strikes." Signature strike is a drone strike that isn't based on the identity of the target. These are strikes against people who "fit" the signature of what the U.S. Government says is a terrorist.
"In Unmanned: America's Drone Wars director Robert Greenwald investigates the impact of U.S. drone strikes at home and abroad through more than 70 separate interviews, including a former American drone operator who shares what he has witnessed in his own words, Pakistani families mourning loved ones and seeking legal redress, investigative journalists pursuing the truth, and top military officials warning against blowback from the loss of innocent life."