the thing is most people who self dx do not have the avenues with which to get a professional diagnosis. seeing a psychiatrist isn't free. getting medication isn't free. but when you start finding information yourself and realizing there are reasons you have felt the way you have or did things they way you did, and people called you names or worse for those actions, it can be rather freeing to realize it isn't you, there might be something bubbling under the surface.

self dx-ing can also be, in other cases, the first step towards pushing oneself to get a professional dx. a lot of people get in denial about that stuff, and you can't just sign up for a psych appointment the next day, and the psych isn't going to know what you have instantly, either. doing research ahead of time during the waiting period (usually months, if my experience is anything to go by) can help move the discussion along when you do get that appointment and make it less of a waiting game while they try and figure you out. it can also help your understanding of what they might be talking about, or if they say something you don't completely agree with.

besides, a one hour doctor's appointment is not adequate enough time to get to know someone you have known your entire life. doctors are not infallible. medical misdiagnoses are horrifically frequent and psychiatric ones happen just as often.

it's not as if a self dx'er is going to go to the pharmacy and grab drugs to self-treat, either. I really don't understand why people find so much harm in this.