What dangers present themselves when someone uses the grounding system as a neutral?
Unlike the European   double-insulated 2-wire single-phase distribution system, the American single-phase system implements safety by using a 3-wire system consisting of a 'hot', a 'return' and a 'ground' wire. It takes just 4   milliamperes of current to flow from the 'hot' to the 'ground' to activate the ground-fault circuit interruption of a well configure 120 VAC power distribution circuit. Any more than 4 milliamperes results in sufficient current to cause cardiac arrest in large people.

If you are using the ground wire (green) as a neutral, not only do you have an unsafely configured AC power distribution circuit.  But also, you do not know what "else" is between the green wire at the point you tap it and the point where the green wire is bonded to the return (usually at the panel).  Almost all electrocutions that occur with swimmers swimming close to marinas occur because some electricity is returning via the green wire (faulty boat or marina circuit).  DO NOT DO IT YOU COULD KILL SOMEONE IN YOUR HOME!!!