Everybody must get stoned?

I just received this email from a 'concerned reader':

Whats with the huge number of stoned construction workers in Vancouver? I walk by 'the Vine' on Broadway every morning around 9:00am and there's usually a group of guys in hard hats smoking weed on Vine street. When they're being more discreet they stay in the alley or in parked cars, but EVERY morning you can smell the smoke along tenth avenue, and this is far from the only case. Along 8th I've seen (and smelled) construction workers, renovators and landscapers smoking up in the morning, and friends that live downtown have told me that Nelson park often has construction workers taking 'smoke breaks'.

I'm not opposed to anyones personal choice about leisure activities as long as it doesn't affect me. I like to unwind with a beer after work and smoke occasionally, but I can't imagine smoking up first thing in the morning and then trying to get work done. I don't work in construction, but I'd think that being stoned around cranes, scaffolding and heavy equipment would be downright dangerous.

Never mind the theory that the dope trade contributes to irrational housing prices, whats it doing to construction quality?