Recently some damage was caused to the turf at Castlerigg stone circle by someone lighting a fire in the circle. It turned out that the person involved was doing something from their own culture with the consent of local people. But does the consent of 50 randomly-selected people count as informed consent with awareness of the implications? The organisation and person involved have apologised unreservedly. However, it is never okay to light a fire directly on the ground at an ancient site, because it might damage the archaeology, and in some cases, the rare lichens on the stones.
On Sunday I visited Arbor Low in Derbyshire and found a firepit scar just outside the henge. I hope that it wasn't Pagans who were responsible for it - but we are the ones who will end up getting the blame in the minds of the general public unless we take a very clear stand against this sort of thing.
At the Rollrights, there is a large metal fire-dish available for use when you hire the site for rituals; this does not scar the turf or damage the archaeology.
We don't ultimately know exactly what the purpose of stone circles was (though we can make educated guesses based on ethnographic parallels), or whether the practices and beliefs of their builders bear any resemblance to any current culture, whether it is "PaleoPagan" or part of the Pagan revival. So we can't just waltz in and use these places just as we like (this also works in our favour, as for example, in 2000 when some Christians wanted to place a rock carved with Alpha and Omega right in the middle of Mayburgh Henge, and planning permission was rightly refused; there was also a peaceful Pagan protest at the installation of the stone 100 yards from the henge). Stone circles are part of the heritage of everyone in this country, and are not there to be hijacked by any particular group.