The Space Shuttle SRB's are ablative nozzles, NASA considers them inherently safer than regen or radiation cooled nozzles.
I dont think thats a fair statement to make about Rutan's design.....
Have you read the test pilot's writeups about the nozzles and every one of the flight debriefs? I did, from the perspective of a guy who's flown high performance aircraft for over a decade now. The nozzles ablate very unevenly, with the same effect of random thrust vectoring. It exceeded flight control authority on at least one flight, possibly two. They came close to losing at least one flight due to the nozzle design. And that was the test pilot saying that, not me.
Ablative nozzles are not new, but in a single engine design like spaceship one, they can be hazardous. In the space shuttle, NASA compensates with another million pounds or so of thrust from gymballed nozzles that swivel to keep things on track. Spaceship one has no such option... 'Mr. Toad's wild ride' comes to mind when describing what it must have been like to try to keep that thing going straight.