Internet forums have always been full of contrarians who want to be the only ones to know the “real truth”. That explains a lot of it. Others just get lost in the logic of it. I’f I can’t prove that he held true Nazism in his heart when he did it, does it count as a Nazi salute?’ This is sort of futile question they ask. The fact that there’s broad consensus on what this was makes them more likely to try to logic their way into a special minority position.