Having used aires since 2003, we have never come across such actions. We have seen badly emptied cassettes and badly emptied black tanks with toilet paper and even worse left over on top of grilled grids and on car parks, not aires, We have seen many times toilet paper in bushes, but not enough from emptying a cassette so probably from a car user. (I hope)
Maybe we have been lucky!
Over the last 10 years, we have pretty much exclusively used aires and wild locations in mainland Europe.
Campsites for the little in the UK
edit
My pet hate, is when as is usual, a Frenchman dumping his cassette and using the drinking water tap for rinsing, when there is a suitable alternative