These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
What an Idiot: Yes, the Geneva Convention does permit that enlisted POWs can be compelled to work, but only work in specific industries that do not help the enemy's war effort, otherwise they are exempted. Such exemptions include public works projects that are military in nature, which the bridge definitely fits. Colonel Nicholson should really have realized that. (Of course this could very well be Artistic License.) In fairness, they do mention that the bridge will serve some non-military purposes such as transporting their wounded, but it really should qualify.