Jingle Bells, jingle bells, I'll have a pint.

Reading the paper this morning there was one of the 'Pagan origins of Christmas' pieces which do tend to be used as filler at this time of year. One of this things in it really gave me pause for thought. Apparently, right, in Lapland, warriors and shamans would feed poisonous-but-psychotropic mushrooms (Amanita muscaria) to reindeer. The toxins would be processed by the reindeer metabolism and the psychotropic bits would pass through and come out in their urine, which those wacky Lapps would then drink in order to get high.

There are a lot of questions that this sort of thing begs, but the one which I most want answered is: Whose idea was that, eh? Who first looked at a poisonous mushroom and a reindeer and said "Hey, lads, this might seen a bit odd, but bear with me because I think I've got a great idea".
And, more to the point, why weren't they restrained for their own safety?