Like Naomi, I've had a personal experience of clearing up after them.
I've told this before...
A few years ago a number of caravans, cars, vans and trucks appeared overnight at the rugby club I'm a member of; the police weren't interested (of course) and it took some time to get rid of them.
While they were there the club had to shut resulting in a loss of income, the local pubs had to close because of the trouble they caused, local shops were the subject of theft and intimidation and the crime rate in the area went up - and these were the things I was aware of, so I suspect there were other local problems.
When they left the rubbish they left was off the scale - piles and piles of it including loads of used nappies and used toilet paper. From memory it took about half a dozen skips (at the expense of the club) and loads of volunteers to clear the rubbish.
The pitches were churned-up and it took months to get them into a playable state and all home matches had to be played away, which also affected the income of the club.
Anybody who thinks they are not detritus has had no personal experience of them.