There's nothing kneejerk about it. Using mocap for the Thing would allow for more flexibility on the filmmakers' part, and allow them to accomplish more with the character in action. The Thing looked decent in the first two movies, but I'm going to have to disagree with you on his looking like an Alex Ross painting come to life. In the Ross painting, the Thing looks like he's made of rock (or whatever rock-like substance he is, I can't remember now). In the movies I thought he looked like he was made of rubber. But people see things differently, so I don't see much use in arguing about it.