This is one of these topics a person could bet on the hand wringing and righteous indignation, and win, every time.
IF a person in an RV pulled in with FULL tanks and dumped on the ground, that would be a mess until it all was absorbed. And they would be the ones sitting in it. For the most part, people do not drain from the RV onto the ground, simply because we can store it easily and dump at a designated location. There are those that have a garden hose attached to the end-cap and let the water run out onto the ground. If a person is going to be parked there for any length of time, sooner or later...that water has to go somewhere. There's only so much room to store it.
The only time grey water smells if it has been sitting in the tanks for a fair length of time. It doesn't just start smelling the second it goes down the drain.
And yes, in many places it is illegal. So is speeding, over-weight rigs, a beer in the drivers lap, littering, etc, etc, etc. All those who never never ever do any of the etc's? you go to the head of the class. The rest of us, get to use common sense.
Gary Haupt