I also find it maddenig when people jusg search for a test online and go: I must have xy because I am had a high score on this quiz.
I just got diagnosed by a therapist how rolls with the the diagnosis of AvPD(or it is still a theory). Though I couldnt give any less fs for the label of my problems. They are what they are and as you said, a diagnosis is mostly used as an excuse rather than a directionary to find help. But like it was already mentioned in a comment on your post, diagnosis seem to differ from therapist to therapist.
Most people dont find the courage or the chance even to go to a therapist. So they do what we all do when we need reassurence for something: The internet. We all try to find answers. Those people never mean to offend those who got diagnosed with a mental disease.
I know that people tend do say sentences like:Oh im just laying around all day! I have a depressiv episode
While their probably just lazy for that one day. I used to get angry when someone said that because I've had clinical depression at that time and tried to off myself many many times. But lets be real. There is no need to get angry because of that. Its just a waste of energy. Just let them think what they think.
And who knows? I believe there are a lot of people here who never saw a therapist because of AvPD. Its the same with people who have SA. They probably run around all those years never really takling their issues.
Even when they have no real diagnosis they still could learn from posts on this site or this forum in general. They seem to have problems with something so why shouldnt they search in a forum for help where there are people with similiar problems even if they dont have all the problems someone with AvPD has.