You know, I'm not sure that's a counterexample. If there were six good and careful coders, I think I could be convinced that they'd make a more reliable system than a few hundred broken into several carefully-spec'ed and rigorously documented teams, where it would be much harder to avoid having a few bad apples, not to mention the impossibility of having even a general idea of what someone else's code is doing.

It's not a guarantee, no. But I don't think it's a knockout counterexample, either.