This comes across as an attitude of, "Too damn bad. Everybody's got problems. You just have to tough it out and deal with it."
This is also an attitude not uncommon towards people with severe, clinical depression or debilitating anxiety attacks. Common, that is, to people who haven't suffered those problems. They too cannot believe that the person who is suffering has a very real illness, an organic, medical condition quite distinct from the daily travails of life, and insist on comparing the disease to their own experience.
I don't see how that attitude implies they don't think it's a real condition. I think what he's saying is it's a real condition with no solution. Maybe it would come across better if he was comparing it to something like... someone born without legs. They know they ought to have legs. It's totally natural to want to have legs and to experience anguish about it. They can get prosthetic legs and maybe that will make them happier. But there are people out there born with useless legs that have come to terms with that and are happy. Others who never do.