Uncounted people use drugs recreationally every day and lead normal, productive lives. I personally know mothers, fathers, lawyers, labourers, engineers, teachers and musicians, all of whom do (or have) partake(n) of illicit drugs regularly with no negative impact on their professional lives.
In the specific case of the musicians I spoke of, was the habit an advantage? No, it was simply, like all the others, a lifestyle choice. They created great music without the use of drugs and equally great music with. Would these people have greater longevity without the use of drugs? Probably, but generally not because of any interference with their professional lives, but rather simply that it's an unhealthy lifestyle and you're more likely to live a few years longer without partaking of substance abuse.
As for disregarding professional achievements, particularly in the case of individuals within the arts to which you refer, that's one of the stupidest things I've ever heard. The work has been produced. What matter the circumstances under which it came to be? Take the lawyer I know, for example. If he successfully argued a case on your behalf, would you like to see the result overturned because it was revealed he'd taken illegal drugs? Do you demolish the perfectly sound bridge constructed by the engineer because he was shooting speed to get through his 16 hour days? (If the answer to either of those questions is yes then I want some of the drugs you're on.)