Like most people, when you walk into the dealer you will be talking to a service advisor. Most SAs are not mechanically inclined but you would not know it by the bilge they spout; such as here.
The only health hazard when machining rotors is if the tech drops a rotor on his foot or gets his shirttail caught between the rotor and brake lathe cutting bit!
Rotors on most late model cars are thin and there is not much to cut. Cuting rotors below the minimum thickness spec makes it a safety/liability issue.
Also, the cost of machining (flat rate time X shop hourly rate) makes it prohibitive and it's more cost effective to replace them rather than spend money machining and wind up with thin rotors.
Hope that helps 'splain it anyway.