...I'm willing to bet that the concession speech was a rare moment of McCain actually saying what he thought and speaking kindly....
It was all overshadowed by the booing, hissing, embittered crowd of sore loser Nazis who even seemed to worry McCain. That might be why you're picking up the evil undertones.
Yes, that's pretty much it for me: he probably was saying what he thought and speaking kindly, but I think he has some PUMA-style supporters who needed to hear a much different speech. Maybe it will turn out that this was OK, but I listened from the booers point of view, and he didn't speak to his angry supporters at all -- they all just got whiplash, or worse: that McCain was just saying what he had to say, and it all had nearly the opposite meaning.
Again, my post wasn't in McCain's voice. It was how that booing skinhead heard those words. I fault McCain only for ignoring his worst supporters and giving a speech which must have inflamed them. Did he do it on purpose? No, I'm not saying that, and I don't care if that was his speechwriters' aim.