IF a circuit is fully loaded (but not overloaded) then there might be 1
or 2
(or 3) volts difference between the WHITE and GREEN wires.

That doesn't matter. There's no current in the green (or bare) wire.
There *is* current in the white wire. Using one's own body to provide a
secondary path to ground for that current isn't very smart.

Don't be silly.

A few volts will not harm you. It doesn't matter whether the wires are
carrying no current or are carrying many amps.