what would you do? See the punches coming and just sit there and take it in the face? Seriously, turning your head so your opponent can't hit you is pretty smart to me. Isn't that the point of fighting... to avoid damage while inflicting as much as you can? Unless you think being hit in the face like a man is somehow the right way to fight.
Yes, I would lay there and eat punches. 'Cos I'm that tough.
But you missed my point. Hansen was throwing legal punches. But then Aoki would turn his head in the middle of the legally thrown punch, and look at the ref expecting Hansen to be penalized or something... The commentators even made note of it. It was pretty weak.
If he had done it in defense as you note above that's fine. But then when he adds the Hey-ref-I'm-FancyPants-Protect-Me look at the ref, that's where it gets shady.