i think you're misunderstanding my point. i'm not saying people shouldn't seek out professional help or get diagnosed, i just think that if someone is clearly depressed but hasn't had a psychologist be like "ya youre depressed" they're still depressed. there are a lot of ways to help yourself with your symptoms of depression but obviously it's important to find the root cause of it and to get treatment.
self diagnosing depression/realizing you're most likely depressed is a part of realizing you need help. people go to a psychologist once they suspect they have a problem and for that to happen you have to know that you can have depression. most of the time depression creeps up on you until it's the new normal and it can be difficult to know what you're supposed to feel like when you're not depressed. so many people treat feeling empty, being sad all the time and hating yourself as normal parts of growing up and being a person and it normalizes it. experiencing those things once in a while is normal, but when you accept that life is just supposed to feel meaningless and terrible and that that's normal... you're not going to get better. In order to get better you have to know you have a problem, and helping people realize that they do have a problem starts with how the general population views and treats depression. if it is a problem Other People have then well, of course you can't have it, you're just tired from a long week! but if it's something you are allowed to call yourself, if it's destigmatized and a normal problem (which it most definitely is, many, many people are depressed), and if it's acceptable to be depressed, it will be easier for people to get help.
i think your view of it being unnecessary to self diagnose is based on just one perspective of the issue. even where healthcare is free there is a stigma, many people don't know they even can get help, their parents might not allow it, they're too embarrassed, or the queue to seeing a psychologist is long. besides, a big part of the tbt community is made up of young americans. in the us healthcare is expensive and if they're poor or their parents aren't supportive it suddenly becomes a lot more difficult to see a therapist and receive that golden Depression Certificate.
seeing a therapist isn't a magic cure, it takes a lot of time and effort to become healthy again, and for some that might never happen. what is important is to learn how to manage your depression. you don't go to therapy and walk out cured, you go to therapy and learn how to help yourself so you can survive all those other hours of the week when you're not in therapy. while it would be absolutely great if everyone with symptoms of depression would be treated by a psychologist, that's just not the way things are now. there are plenty of depressed people going undiagnosed and without help, these people still need and deserve support, tools and understanding. not gate keeping depression resources, communities and self help things is super important for people to get better.
of course people should seek help, especially if they are having more problems, it's very persistent or it gets worse. you don't know exactly what's going on with your head and there is definitely a risk of it being something other than organically homegrown depression.
you seem to be concerned about people being mistaken and self diagnosing with something they don't have, which definitely can happen. i'm not arguing against that, i just think that gate keeping depression is very harmful.