The other thing Big Dog can (potentially) do that a mule could not is fight. You can't armor a mule, or mount a grenade launcher onto it and expect it to do well on a battlefield, but I fully expect that that's at least part of what they have in mind for Big Dog. It can't be a secret that the Pentagon would eventually like to take its human soldiers out of harm's way entirely.

Of course, the real reason this is unsafe isn't because it offers poor head protection or restricts vision. It's because 40% of the people who buy them will do so with the intention of setting them on fire and then riding around attacking evildoers with a 60-foot chain.