Rather than harmless, what the lawnmower analogy achieves is to make him seem blameless. "How can you assign blame to a thing that's just doing what it's built to do without any intent?" It's important to push back against that. Intent isn't a necessary condition for something to be dangerous, and so it's not necessary to ask whether it is intentional or not. A rabid dog will be put down regardless of who is to blame for it.