Morality and efficacy. It would be really rude and irresponsible to send metal crap all over the universe. It may also be really bad for Earth if we eat all of

Morality and efficacy. It would be really rude and irresponsible to send metal crap all over the universe. It may also be really bad for Earth if we eat all of Mercury. Figuring out the question of "how much mass from Mercury can we send somewhere else before something becomes a problem for life on Earth" sounds like playing with fire. What if Von Neumann probes kill life on another planet? What if other sentient life meets one and gets offended? Can we even get useful data from a Von Neumann probe that would offset the potential cost of it harming another planet? I don't think it's worthwile or ethical to send such a device into space no matter what is out there.