My Hatred Of Rednecks...

[Thumpalumpacus]

Technically, they can "veto orders".  Or, rather, some are veto'd pre-emptively.  A soldier cannot be tried for failing to comply with an unlawful order.  They also have an inalienable right to miss.

Of course. But the legal ramifications for such are long-winded and expensive. And, more to what I think your point is, a good leader has his thumb pretty close on the pulse of his unit and won't ask them to do the unreasonable?

I received, and gave, a few orders that tested this line of thinking -- but fortunately for me, I knew the guys in the building, and the guys on the truck I commanded, so it wasn't so much that the orders told me or them what to do as they did ratify what I already knew to be the right answer.

Admittedly very different from higher-echelon commands, where complexity and scope of command give rise to deep questions.