Was on orkney recently and i sort of see his point, the beaches there really are covered with these piles. I'm not sure it's a big deal on beaches like skail but if the act becomes really popular then i could see thoughtless and careless people causing ecological damage on other, more sensitive, areas.
I also thought the guy saying that the mental health benefits to humans outweighed any potential environmental damage was an incredibly arrogant statement (and i both suffer from mental health issues and work in the mental health sector so not belittling the problem).
Must admit i got a bit of a therapeutic benefit from knocking some of the piles over :)
Can't stand the bloody things and they're everywhere nowadays. On a recent trip to Santorini I walked to the old castle ruins and the place was littered with little piles of stones for some obscure reason. I presume it means "Oh look at me, yes me". Please get a life or curl up and die, either way will be a distinct benefit to society in general.