I found this question hard to answer, because there's really less compelling reasons for an artist to do drugs than, as per the Jerry Seinfeld bit, an accountant. Yet the acceptability, indeed the expectation of artists taking drugs is categorically different from non-artistic vocations.
A career in the arts, specifically as a content creator - an artist as such, and not any of the peripheral para-artistic careers (gallery curator, record executive, talent scout etc.) - you are pursuing a profession I would characterize thusly:
low odds of success, high potential payoff.
Which is to say, if you were to compare being an artist to opening a milk bar, what you would find is that in the history of milk bar owners, you would find a lot of financially comfortable and secure small business owners achieving pretty consistent standards of living, with a peppering of failures. The reverse would be true in the history of artists, you would find a vast nameless diaspora of failure, people who slowly bled to death or simply gave up trying to eek out a living from their art, peppered with a few well success stories.
But what you will find, is that the best day of being a milkbar owner ever, wouldn't even rate compared to the best day of the successful artist. The potential upside of owning a milk bar, is kind of capped. Can you for example, imagine a milk bar owner's work leading to an email inbox flooded with thousands of messages from strangers telling them how much their work meant to them? Tricky right, you are already imagining heroic acts that have little to nothing to do with the operation of a milk bar, like rescuing a child from a burning building. But I put it to you that it's pretty easy to imagine this happening to an artist, because of their artwork.
Gee, tohm, you wrote a long two paragraphs, but what is your point? My point is, that if you are in the business of being an artist, you are going for such a reward, such an achievement. The feeling of being inundated with the validation of strangers as to just how great your work is. A level of recognition unobtainable to most. You want it, even though it may well be unobtainable to you. You are looking to overload your neural reward systems, reserved for exactly such achievements.
Now take a fairly innocuous drug like XTC, successfully re branded to MDMA. A drug I looked pretty hard at taking. I should say in due dilligence, that I never took it, nor any other restricted substance, probably because by and large my motivations were poor for raising the question in the first place and also because ultimately it breaks one of my ruling rule of thumbs - risking something important to gain something unimportant.
Anyway, the thing about drugs, is that they work and in the short-term they can 'solve' problems. But consider my risks as an artist myself - I have these dormant, latent reward systems waiting for some event in my environment to trigger - kissing my soul mate, having a successful exhibition, running faster than I've ever run before etc. One of these events causes dope to release in my brain hit all those receptors and let me know that I am doing something right.
Or I can take a drug, that hits all those receptors anyway regardless of my external reality. What could be more damaging to your career as an artist?
I'm told, MDMA feels great. And anybody who ingests it, is going to feel something.
But this is also true of running a marathon. The difference being that people who run marathons are less inhibited about broadcasting that they do and they feel people should in the public domain, more so than recreational drug addicts. But in contrast somebody who pushes marathon running, is often regarded as self-righteous, and the idea of spending a year training for a marathon to obtain that high is seen as justifiably dismissable - no doubt because of the time commitment, the difficulty of starting, the demands for lifestyle change etc.
But among artists particularly, despite the demonstrable damage and risks of drug use (legal or illicit) EVEN AFTER discounting damage caused by ineffective anti-drug legislation (eg. when weed possession was still criminal) cannot shake the stigma of somebody who declines the experiment with being 'closed minded'.
Which perhaps is the hook that gets most aspiring artists. they should be open to altered states of consciousness. But before moving too far away from the 'fucking with the reward system' counterargument, let me draw this one last line between running and being an artist (of which I am both) is that it is hard to imagine, and I imagine incredibly rare to find a runner that before/after a run shoots some morphine or other opiate to stimulate the exact same reward response that they get from running.
Yet for some reason, for an artist, in between actually completing and releasing works of art that they should stimulate the exact same reward centers through cocaine or MDMA. I can imagine, because running is addictive, injured runners getting hooked on painkillers, certainly, but I don't hear of runners taking painkillers in the off season.
Believe it or not, I often actually argue with myself. A lot, and most of this is done before writing a blog or conversing with a friend. And the best counter argument I could come up with is that the analogy is a poor one. One could argue, that recreational drug use is to an artist, what training is to a runner when compared to the actual marathon.
There's even that Bill Hicks bit that featured on the Aenema recording of Tool: