I'm not going to get into a debate here - partly because this isnt the place for it and partly because it's going to be an uphill struggle explaining things such as the fact that alcohol is not a stimulant, but a depressant. And also that known stimulants are regularly served on the flightdeck without creating any decline in performance... some would report an improvement in these times of fatigue and increased sector days.(re: "stimulants (of any flavour) have no place on the flightdeck"). And best not get me started on the economic and political reasons for the criminalisation of "mind altering substances" over the last century!
As for drawing line.. well that's up to individual's ability to make sure nothing he does adversely effects his ability to do the job. Personally I'd err on the side of abstinence - also i'm quite happy without these things. I certainly don't see how the occasional line of cocaine or even ingestion of heroin is any worse than the occasional night out on the booze.
Also with regard do the drawing the line theory.. would that not mean that you'd "draw the line" before alcohol, coffee, paracetamol etc? You've already admitted that you like to drink alcohol.
But as Wbryce says it's an emotive topic and opinions are bound to conflict. Whilst i respect all opinions it's important that they're backed up with knowledge and experience rather than, for example, what you read in the paper.
Aargh.. really didn't want to derail the thread, damn will-power... final post!