The desecration of many upland cairns is possibly due to the misplaced idea that "treasure" of some sort could be found there. The ones that I've seen that seem to be in their original condition are far from the beaten track. The one I mentioned on Deelish requires some effort to reach, involving wading through waist high heather which covers an ankle breaking litter of moss covered rocks. That is in itself a deterrent to those intent on elusive riches. There may be in some people an inate desire to just shift stuff around, something I've never shared.
As for the Irish Dlomen s? (What exactly is the plural of dolmen??!)
I've always had a problem with the idea that these were covered with mounds. If they were, and I've seen no evidence to prove conclusively that this was so, why did the mounds covering the dolmen vanish when other mounds did not? And if they were covered with mounds, how would anyone know what was underneath? It seems strange to me that if these mounds existed in the first place, why should they have exclusively vanished, whilst all other mounds (i.e. Knowth, Dowth, the English long barrows) have remained in place? Once a mound is in place, it seems to remain so.
To me it seems to be an oft repeated piece of conjecture, dreamt up by some academic in the last century, with no supporting evidence whatsoever. But because it was forwarded by some luminary or another, it has never been challenged, and remains "accepted" wisdom.
No evidence has ever been produced to support the mound theory, and in my opinion, limited though it may be, they never existed. The dolmens are a striking feature in the landscape, and were meant to be seen. To go to the considerable effort to build them in the first place (and if you ever get to see the example at Kilmogue in Co. Kilkenny, one of the most remarkable pieces of balancing in western Europe, and one that would defy the most modern structural engineer) and then to cover them with earth, seems ridiculous.
But then, so is the proposition that the stones at Arbor Low were blown over by a wind. It was a remarkable class of a wind that arranged the stones thus. Its clearly a recumbent, and has always been, despite the nonsense spouted by Burl. But archaeology, and that conducted by upper class twits inparticular, who were obviously unfit for any meaningful employment, needs a reappraisal on many fronts. Something that the present occupants of the ivory tower are reluctant to do.