In reply to Anonymous:
> I see a lot of morons (not you, I hope ...?) dragging mats around the dustbowls at the bottom of crags, and throwing them through foliage rather than carrying them more carefully, and that's why I raised the question.
That suggests that it is the (mis)usage that some people put bouldering mats to is the cause of the problem - ie they don't think of the consequences on the environment of the way they behave... They probably drop litter and fag-ends and don't clear them up either...
So, it's people's attitudes that are the main part of the problem - the attitude that has been awesomely demonstrated by some people on this thread...