I had a similar thought with Foreing Dispatches when I read the post on the Marmot about the Korean missionaries in Afghanistan. Historically Chiristians came to Japan to convert Japanese Barbarians as
well as to, it is said ,colonize the nation. So it is not surprising that modern evangelicals have acted like that. But I was not sure of it because of the story of Mormon missionaries on the post.
I am not sure if Japan was lucky or not but I think it is hard for an average native Japanese to hold the idea of the absolute God so jealous as to forbid to worship other eight million kami(gods)
At best even believers would, deep down in their heart, think such "God"is just one of the great gods, I suspect.