I know they considered it dishonorable and cowardly. I assume the bushido code was a consequence, rather than a cause. Perhaps that's a false assumption. From a technological development point of view, it makes no sense at all. All pre-gunpowder military doctrine evolved around the shield. Greek hoplites, Roman Legions, Persian Immortals, Medieval Knights, all used shields. The Vikings, who had no contact (I presume) with the Europeans before the raids on England had shields. Mayans, Africans, Indians (from India), the Chinese... It seems the technology developed independently in several areas, as well as proliferated through geographic proximity. The Japanese seem to be the only warriors not to use it. Why not?