We have a death-penalty debate in the US, which has consequences for less than 100 people per year. We have a few hundred thousand people serving sentences of 20 years and up, but no debate about it. That shows that most Americans place a huge value on life itself, and almost no value on what happens to that life.

Another reason might be the possibility of judicial errors. You can release a locked-up convict and compensate him somehow, but you can't resurrect a dead convict.

Edit: my comments below this line are irrelevant to the point of this discussion, please disregard them.

Killing enemy soldiers is allowable; killing enemy civilians is not.

One can't win a war without killing enemy soldiers, but one can win a war without killing enemy civilians (modern wars tend to somewhat blur the line between combatants and civilians). Also, killing civilians motivates enemy soldiers and stimulates the spontaneous formation of militia.

Killing enemy soldiers is allowable; torturing them is not.

Torturing enemy soldiers doesn't help you win a war and may motivate enemy soldiers to fight to the death, or to torture your own soldiers in return (let alone PR disasters that may arise out of this).

Losing a pilot is not acceptable; losing a $360,000,000 plane is.

Not sure what plane are you talking about. Also, the total costs of training a pilot may well be in the millions. When you officially devalue the pilot life, you're sending a message to other pilots which will tend to avoid dangerous missions, or just drop the career. (Also, unmanned flight will make the problem obsolete).

My personal position: any life is valuable. Murder is not acceptable.