I'm not sure. He seems to add a lot of caveats that indicate he doesn't necessarily believe the stories to be real (emphasis mine): "I do not know whether I s

I'm not sure. He seems to add a lot of caveats that indicate he doesn't necessarily believe the stories to be real (emphasis mine): "I do not know whether I should believe this; if it is true, I do not know whether we Germans are not really devils instead of human beings. It must be admitted that there are some extremely coarse and wicked people. The devil is never idle. My advice is that if any such persons are discovered" I think he did know that the plague was spread by something physical. He talks about fumigation. And he's not wrong to say that social distancing is preferred. He doesn't seem to be any different from people condemning spring breakers in Florida who have outright stated that they don't care if they get the virus. His reaction is more extreme, but he was saying that if such people are blatantly infecting others with a known deadly disease and laughing about it, they should correspondingly be punished with death. He is not suggesting that he himself or anyone individual should execute them. He is suggesting that they should be punished by the authorities by death. Calling them devils, if I read in the context of the whole thing, he seems to be using hyperbole, not sincerely believing them to be supernatural beings, but rather, just something evil the way that some people may call serial killers or morbid gang members devils. He does say that such people could be influenced by "the devil", a supernatural being, but that's not a huge surprise, given his beliefs, and it's certainly not something he dwells on. If he truly believed them to be devils instead of using hyperbole, I'm sure that his recommended remedy would be something along the lines of prayer and exorcism for them, not hanging. Rather, he focuses on the behaviour and the corresponding punishment, not the supernatural. If he focused his letter more on the supernatural than he does, I'd be inclined to agree with your conclusions. Like I've read some American preachers apparently talk about COVID-19 in a very religious vein, much more than what I see in this letter. Those people really focus on the religious stuff, not the physical behaviour. I don't see that in Luther's letter. Given what I've read here, I think he is focused more on social realities and talking about hypothetical criminals and capital punishment in a modern sense. He does use religious language and logic to explain his points, but I can excuse him for that, given his background and occupation. We need to be able to understand whether our interpretation matches what someone is intending to say, it's very easy for our interpretations to be wrong, especially if one is using hyperbole. Yes, I could be wrong too, of course.