First of all, I have never used illegal drugs. That being said, I have two concerns:
1. Most "drug testing" is useless
a. Easy to defeat - Examples are even on this board where there was a big discussion of many ways to beat it.
b. not reliable - I personally know of many false positives that had serious consequences
c. Just for show - I saw signs at Home Depot and the grocery store that emphasized that they drug test all applicants. In reality, I would prefer that the person giving me gardening tips was growning his own private "garden" As far as the supermarket, are we afraid that the coke-head stockboy won't look like he eats enough of their products? Isn't he the safest guy since he won't be sampling the food?
2. "Just say no" is silly
a. Prohibition doesn't work - see Prohibition in the US
b. If "saying no" would cure the problem, then explain Darryl Strawberry and Robert Downey, Jr.
c. We don't have a "just say no to eating paste" or "just say no to painting others with gold paint" yet most people grow out of the paste eating stage and only Aurius Goldfinger has painted someone with gold paint (and Mr. Connery took care of him)