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.
It seems that is suggesting it's OK to climb on the stones if you're an expert in rock art elsewhere and/or a jovial sort who laughs in the face of conventionality.
I disagree about the "unconventional and jovial" justification, it just means people that don't care what others think. As for the expert bit, have these marks been accepted as man-made by anyone other than this group? Maybe they got it wrong, and they're natural? One of them said - "the majority of Wessex archaeologists are academically illiterate when it comes to identifying such carvings". Sounds like "Wessex archaeos don't agree they are man-made" to me!
I'd certainly hope they don't care what others think, go at it with a clear and open mind without looking to any sort of "peer" for justification or a pat on the back, that's the very thing that is holding modern archaeological theories and interpretation back.
Archaeo's never take a positive light on anything, unless they're the discoverer and there's something in it for them.
I could point you in the direction of newly discovered sites/ra that the area's archaeo's refuse even to visit. !