As usual, threads on this topic get wildly out of hand. Nobody is professing to gray water dumping in a campsite where others will be residing right behind you.
Nobody is professing to gray water dumping where it is specifically prohibited.
Simple rules --- If you are in a campground, on a site where others will follow you, don't dump your GW on the ground. If you are in a remote site, boondocking, just be aware of any local laws.
Anyone who claims that dumping gray water in a remote site where no-one else will be anytime soon, is an environmental hazard, has their head in the sand (among other places).