Yes, very rough. Marijuana still being illegal at the federal level, and often illegal at the state level, means it's not always in your best interest to self-report.
For example, in my doctor's questionnaires. "Have you used illegal drugs in the last year?" I'm always going to say no. I don't trust security and privacy enough to say otherwise.
And yes, for HN scrapers, I'll mention this is all hypothetical.
Not sure how much it differs from the US, but in Australia disclosing previous drug use is unlikely to provoke any response from authorities. The main drug crimes are possession and selling AFAIK, not using.
True! But insurance companies (in the U.S. at least) would also love to know that information...