This is thought-provoking but in the end missing one key point I think. The trainees aren't told that trying anything is trying anything is futile - although they might believe it is so. If they end up trying to save the civilians, fail, and then in the debrief they say they never believed they had a chance bt felt they had to try that's not a captain you want. If they didn't try but didn't seem bothered by the abandonment you don't want that one either. If they thought through the options and realised the odds were too slim but they were haunted by the worry there was something they hadn't considered, that seems like Starfleet material..