two very probable cup marks previously unrecorded. :)
http://www.themodernantiquarian.com/site/25/devils_den.html
I suppose the question is 'does the means justify the end'. In the great scheme of things no damage was done. It sounds like you might know me so you will also know I'm not the sort of person to start laying down the law to others - even if I don't agree with their actions. Had I thought damage was being done I am certain I would have spoken up - as I'm sure you would have done too.
700m North-ish lays the cup marked stone tjj, formerly the only known (though disputed by some) example of rock art in hundreds of square miles, with experience you learn to search out any significant other local and obvious features to explore for further examples.
I'm sure you've seen none of said above people show anything but complete respect for the Avebury area stones on any other occasion, and indeed champion their preservation.
In general i agree with you, but also it depends why you're climbing on the stones, and who is.
I understand that day, from what i've read, you had with you what could be classed as the 3 foremost experts on rock art in their respective areas. ?
Inquisitive jovial sorts who's laugh in the face of conventionality. :)
x...peace...x