If you were to have some construction work done on your property, lets say window replacement or a driveway replacement, would anyone be comfortable if they saw the workers down a 40 and/or smoke a joint on their lunch break? I'd be on the phone before they could get another ounce down their throat and tell the owner what's going on. I bet you those guys would be canned on the spot. News of that starts spreading that owner is losing jobs/money.
When you're paying good money for a project you expect the workers to show up and act professional.