Nope, quite sane. Amazing, though.
> The lateral forces have to be enormous. They must dig a deep hole to support it...
Well, yeah...
> Wouldn't want to be around one during a major storm...
I'm certain they feather the blades. The rotor doesn't get going very fast -- with that big a blade, the tip speed approaches the speed of sound at surprisingly low RPM. Consider, if it's 341 feet diameter, the tip will hit Mach-1 at one rev-per-second. 60 RPM.
So you know they keep it below that.