Tim,
I have no idea who employed you, but I suspect there are VERY few jobs where taking drugs (off-duty, anyway!), or even being prosecuted for druggie no-nos, ACTUALLY affects your ability to do your job.
The few jobs where this is an issue, I would bet it is all about "image". So it's what other people think, or CLAIM to think.
e.g. headteachers can easily do their jobs and snort coke on Sunday mornings. Unfortunately many parents would disagree with me, rightly or wrongly. Many parents would also object to a gay/jewish/muslim/female headteacher...
I would like to watch the BEST sportsmen compete,
NOT: the best sportsmen who also have a squeaky clean private life.