Incidentally, you mentioned "none of said above people show anything but complete respect for the Avebury area stones on any other occasion" (which I assume means they don't normally advocate anyone climbing on the Avebury area monuments) so I'm curious why they felt it was justified in their case on this one occasion?
It's also about association, in this area it's one of the less visited sites, unlike Avebury itself, Silbury, WKLB, WKA etc etc which have been scrutinised inch by inch, and as already said, 700 metres distant you have the only other of possible rock art in the area.
Personally, before reading an online article a month or so ago, i'd never seen those markings so it was of interest to me, i've since climbed the monument myself and taken further photographs as i strongly believe any markings no matter how debatable should be recorded for posterity and further scrutiny, if that means a few well informed people climbing a monument for all the right reasons i fully support them, they've come up with the goods in the past.