Thank you, that is indeed food for thought. I would certainly agree that many of the stone cairns I have encountered have been vandalised, dug into, and generally disturbed. There are two however I have come across which appear to be in their original condition. One is below Crohan west in the Knockmealdowns, and the other on Deelish mountain in the Comeraghs.
If I may explain.
The two mentioned above are not random piles of stones, but appear to be carefully constructed. Both have dished interiors, but both have distinct features within them. The one on Deelish is the most interesting, with a crescent shaped "entrance". Inside the dished interior are are two "ante chambers", that is to say, two seperate compartments to the cairn. Whilst some stones have fallen, or have been disturbed by livestock or walkers, the essential features of the cairn remain intact. Others, notably the one on top of Temple hill in the Galty mountains has been seriously brutalised in the not so distant past. Others have been damaged to a lesser extent, but seem to have similar distinct "compartments". What they represent can only be speculative.
My reasons for doubting the wind shelter theory is this. In all the years spent tramping these mountains, I tend not to go up when the weather is bad, bordering on the dangerous. This is only from personal experience, but when I do see bad weather coming in, I get the hell out of there. At no stage have I considered building a shelter, when in a quarter of the time I could be back in front of the fire at home.
Its my belief that the "wind shelters" had some other function, because most of those I've encountered would do little to promote a persons health or well being.