To my mind there are two quite separate issues here, but they are being treated as one.

A professional "artist" demands money from the public: they in return have a right to see the artist's skills displayed professionally and competently. An artist who can not do that should not be appearing.

There are many reasons why an artist may no longer be competent at the required level: alcoholism or addiction are not the only reasons. They are not the reason why other giants of the 60s such as Muhammad Ali, Bobby Charlton, Jackie Stewart or Nic Jones no longer "perform". There comes a time when it's best to say "enough", whatever the cause, allowing your public to remember you in your prime.

BTW - I've never seen Davy Graham perform, and therefore have no useful opinion on his competence: if he's still good enough then by all means carry on.