Weed is a part of a lot of people's lives. It was part of mine for years and probably had a net negative effect. I like it too much. And I'm not good for much afterwards other than eating cheetos and watching Ren & Stimpy. Forget playing. I've never been shocked by fellow players firing up, it's just somethng that's around. I don't quite get the OPs level of shock but I absolutely get the frustration over the guitar player's playing suffering. Could be some confirmation bias at play but I've also seen plenty of folks whose abilities plummet after taking a substance(and they rarely seem aware of it).