For obvious reasons, military institutions like to have soldiers with a ‘can-do attitude’. When you tell your troops to do something, you don’t want them replying that it all looks a bit too difficult, and they’d rather not, thank you very much. You’d prefer to have people who regard difficulty as a challenge and strive to get the job done however impossible it may seem.
That’s all well and good, but sometimes the job is just plain wrong, and shouldn’t be done at all; or it just can’t be done, no matter how hard you try; or it can only be done at disproportionate cost. In such cases, what you need is not a can-do attitude, but somebody who will say ‘Sorry, boss, but this immoral/stupid/impossible, don’t do it.’