This would (possibly) be true if all mistakes were weighted equally. As soon as some mistakes have more weight (like maybe the machine killed you on accident because it thought your spleen was in your ear), then looking at aggregate numbers doesn't cut it. You'd need to look at both the frequency of errors, as well as severity of errors. I'll take the guy who messes up 50% of the time, but at worst will give me a paper cut over the hypothetical machine who only makes mistakes 1% of the time, but they're always fatal.