Arguing about the Geneva conventions is nice and all, but the moment one sides breaks them, they're meaningless.
If an army has been known to use symbols of neutrality like the red cross (or civilian clothes for that matter) in surprise attacks, their enemies rightfully won't care about these symbols any longer.
Except for some truly extreme cases (like Americans mass-executing German kindergarteners suspected of being Werwolf forces), it's more or less understandable imo. Not much point in dying with a clean conscience.