So non-drinkers, (or indeed, anyone without any vices) are quite boring are they?
Yes, people with no vices are usually tediously self-righteous and very boring in my experience. Having no character flaws at all is usually a recipe for a person being utterly un-likeable in my book.

Why would there be a need to have weed users declare it to potential employers? If it makes them lazy or unprofessional, that should be reason enough not to employ them without delving into their personal habits. If not, it's none of your business.