Why are they called stoners?

[Carby]

Why are people who smoke weed called stoners when smoking has nothing to do with stones??

[Quizmonster]

Presumably because 'stoned' has been used as a slang word for drunk - or otherwise intoxicated - since the 1950s. Such intoxication is one effect of smoking weed, so it's pretty logical that people who do that are called 'stoners'...though I've never heard the word so used.
The phrase 'stone-cold sober', on the other hand, has been in use since the 1930s and the idea of coldness and sobriety being connected makes sense.
Maybe weed-users think they're especially "cool" even though they're actually "drunk"!

[barniclebill]

It's just rock and roll....(get it, roll a joint perhaps?)