I keep wondering which planet soap comes from, if it's so unnatural. However, in any given place, it's going to rain enough, especially in the U.K., to cancel out the effect of just about anything short of a gallon of oil being poured on the ground.
Deadly nightshade, European yew, Oleander, Rosary pea, Hemlock all grow naturally on the same planet, you really wouldn't want to go eating any great quantity though.
Even things that seem harmless like apples, pears etc contain trace amounts of Cyanide, many beans contain trace amounts of Ricin.
All natural and all deadly enough of processed or if consumed in enough quantities (you'd have to be pretty determined to eat enough apple seeds to harm yourself)
Earthquakes, Tsunami's, floods, Hurricanes, methane, volcano's, Malaria and a million other things that cause thousands or millions of deaths each year also come from the same planet.
In fact the only thing that i can think of that does NOT come from this planet that causes harm, death and destruction is asteroid impacts, other than that every single death and illness on this planet is caused or is a result of something that comes from this planet.
As i say it's 100% my choice, i'm not telling anyone else what they should or should not do.
It's only basic common sense that if enough people dump even a small amount of a chemical into a small lake it's only a matter of time before problems start to occur.
Rain run off isn't a answer either, as if a lake becomes polluted with human waste (including pot washing detritus and soaps) then all the run off will just go down to the next lake and/or river.
Again this is just my choice when i visit areas that have a high footfall or high rate of campers.
As yet, out of 30 odd years of camping i can't honestly say as i've once thought "i wish i'd bought some dish washing soap with me" so it's not like i'm living any great hardship by mot taking washing up liquid.