They're a ridiculous idea. The stats may support the fact that they are 'statistically' safer (less deaths).
But as my old statistic teacher taught us, "the thing with statistic's is they can tell you anything you want, including 'technically' the wrong answer".
Having seen a lorry hit a car parked on the hard shoulder (fortunately the occupants weren't in it) I'd hate to be in a car that had broken down on a smart motorway, even more so if I had the family in the car.
At least on the hard shoulder there is an escape route, as there's certainly isn't on a smart motorway.
The amount of times I've seen people ignore the Red Cross on the signs, and only take notice when there's a camera on the gantry do they not use that lane.