Of course no one is going to dump it on the ground at a KOA.
offroading does way more damage than a table spoon of coffee grounds, it can be argued that the coffee grounds would help the environment, plus people are pissing and taking dumps, firepits, oil leaks ( one drop would be much worse than coffee)
cognitive dissonance , when two actions or ideas are not psychologically consistent with each other, people do all in their power to change them until they become consistent. This triggered by the person's belief clashing with information perceived, wherein they try to find a way to resolve the contradiction to reduce their discomfort.
No one wants to harm the environment but people are going crazy over things that don't really matter in the big picture, when at the same time are doing things that are much more harmful.
Next will be paper coffee filters, if you don't use reusable filters you're a bad bad bad person and soon a better human will come along to tell you how wrong you are.