Unfortunately, where I live, travellers have a bad reputation. Most recently a group of some 10 caravans broke a gate and moved a deliberately placed tree trunk to access land (a common), and set up camp for five days. Police were involved in moving them on, and they then moved to a nature reserve (again illegally entering). Police moved them on again and they are currently illegally camped on private land belonging to a local religious group.
In the places they'd set up camp they have left broken fridges, mattresses, animal and human excrement and have broken glass deliberately on footpaths.
What tends to anger people is a) the mess that is always left, and b) the fact that there are permitted temporary sites which are not used.
I realise that these people are in the minority but I wonder what you as a traveller, think of this behaviour, and what can be done to improve relationships with the general public in light of it?