I've been puzzling over how we behave when we're away from home. We seem to become different creatures. At home, we (mostly) recycle, maybe even compost. We (mostly) gather up non-recyclables and put them in the garbage. We (mostly) don't drop everything on the floor when we are done with it and leave it there for others to trample on.
When we get away from the nest, however, funny things happen to our psyche. Somehow it's no longer our responsibility to make sure things get recycled or put in their proper places. We litter, we abandon recyclables, we leave popcorn and sunflower seeds all over sporting venues and theatres. We behave like pigs. (Oh wait, I think pigs are actually cleaner...).
Likely part of this behaviour does involve all those inner children bustin' out. But I think there might be other factors at play.
The first that comes to mind is the situation. If there is no place close by to recycle, likely all but the most conscientious of us will choose the garbage (or litter) route. It's not that we are necessarily all barbarians, it's the situation the encourages the bad behaviour. This is a lesson for everyone that wants people to do the right thing. Change the situation (put recycling bins beside every garbage container, and put lots of them around; don't offer disposable plates -- make patrons pay a deposit on a reusable plate that they get back when they return it...) and people will behave like better citizens.
The second factor in our acting badly when we're away from home has to do with our social natures. We take our cues from others. If there is litter all over a festival site, we take that as permission to add our own. After all, what difference is one more cup going to make?
I've even heard of studies where the researchers used accomplices to model desired behaviours and we hapless social animals started to do things the way the accomplices did.
Green event planners would do well to consider human nature: we generally take the path of least resistance and we look around at others when we decide what to do (both good and bad). Designing your event accordingly should make it more successful.