I think it's interesting (and this is by no means an observation unique to me) that we term alcoholism a disease, but continue to blame drinkers if they are not helped by treatment, assigning their inability to get well (sober) to a moral failure of the will (not wanting to stop drinking badly enough). It seems we really only reserve the term "illness" for alcoholics who have stopped drinking, thereby allowing those former drinkers to shirk from the blame for misdeeds while drinking (since it is, after all, an illness). There's a lot of truth to that bit of bumper-sticker/t-shirt wisdom, "I'm not an alcoholic, I'm a drunk. Alcoholics go to meetings."
It's impossible to say why these particular famous writers were given to drink, whether it was the romantic notion of a tortured soul self-medicating or the sign of an egotist who couldn't live with himself in real and sober terms. Perhaps, though, like all alcoholics who continue to drink, these writers deserve some sympathy instead of judgment, some allowance for their humanity, as well as an acknowledgment that their humanity (including perceived character flaws) allowed them to be better writers and artists.