Generals and Privates

First requirement: obey all legal orders.
Second: serve honorably.

Question: Must officers, especially command officers, wait until they retire or resign to say what they think about what they consider to be mistakes ( to their commander of course)?
Should they accept responsibility for a command that they consider operating to no avail?
Or, should they resign or request other duty?
Privates: They volunteered! Wouldn't matter if they had not, though.