There are plenty of functioning lazy people, functioning depressed people, functioning autistics, functioning assholes etc., and all are going to not be their best or miss out on good opportunities etc., just as a drunk would.
A non-functioning depressed person, non-functioning lazy person, non-functioning alcoholic etc., can't hold down a job or take care of themselves properly (i.e., function in society). There needs to be a label to delineate the differences because they certainly are different. Just my 2c