Torture has been discussed here several times and the general consensus seems to be a negative stance towards it, both in term of morality/ethics and of course law.
The concept of collateral damage seems to be a bit harder to put into a single basket, and we generally accept it much more readily.

Sam Harris has some interesting views on this, which I tend to find quite compelling:

…I briefly discuss the ethics of torture and collateral damage in times of war, arguing that collateral damage is worse than torture across the board. Rather than appreciate just how bad I think collateral damage is in ethical terms, some readers have mistakenly concluded that I take a cavalier attitude toward the practice of torture. I do not. Nevertheless, there are extreme circumstances in which I believe that practices like “water-boarding” may not only be ethically justifiable, but ethically necessary. This is not the same as saying that they should be legal (e.g. crimes like trespassing or theft may sometimes be ethically necessary, while remaining illegal).

What say you?