Based on only my English brain's experience with the phrase... "without thought" (as Lighter said) is the meaning it conveys to me. Without much thought, surprisingly casually, without due consideration. The action being done should be something that normally requires (expects) careful decision...like executing someone for example. You wouldnt say you ate supper "out of hand" because you were hungry, but you might marry or enlist in the military or give a criminal sentence that way...which would be atypical... get it?