Hi stubob. You'll not find anyone arguing with the points you've raised. We've discussed them all ourselves. If you look on the Modern Antiquarian web site there is a posting regarding the reversing of a vehicle into it.
It is such a shame when a site gets hammered the way the nine have been. It is years since I have been anywhere near the place, but if what folks are saying is true then the 'protestors' need a good kick up the arse. If they want to preserve the site so badly then let them start by keeping it in good order now, otherwise there will be nothing to protect!
As I say I am only commenting on things I've been told and so if I'm misinformed then please forgive.
9 ladies is quite a high profile site for many reasons and does seem to attract more than its share of ... erm ... twats!
As to why this happens ... I haven't got the foggiest, but like yourself I want to see these places enjoyed yet above all preserved.