I think maybe you've misunderstood what the common knowledge said. Turbulence hasn't ripped an airplane apart at altitude, so yea turbulence alone hasn't caused a crash. But anything near terrain is plenty risky (mountain waves, low-level wind shear). If the turbulence makes you drop a couple of hundred feet that's no big deal at 35,000 feet and no matter how bumpy it gets, the wings aren't going to break off. But if you're near the ground (or a mountain), well....