"as a society we have compartmentalised social life, so that the help one previously expected from his family/friends (and ultimately: from the way he can structure his life) is now to be had from paid professionals (or tacky volunteers)"
What if the depressed person is estranged from his family and friends? Or what if he has none? What if he feels he can't talk to either?
You overestimate the help that family and friends can give, even if a depressed person is willing and able to go to them for help. They rarely have the training or understanding of human psychology to do more than provide the equivalent of first-aid.
Expecting family or friends to help someone overcome severe depression is like expecting them to be able to successfully perform surgery. Sure, if they happen to have significant medical training, they might succeed. But in most cases such expectations are completely unrealistic.