So I'm someone who's very involved with the autistic community in my country (at least used to, taking a break now, not sure when to come back). I'm just gonna pitch in and say that self-diagnosis is more of a symptom of a larger problem: which is lack of access to proper, official diagnoses. It's not perfect, in fact it can be harmful. For example, I know someone online who thought they were autistic and through a doctor who specializes in autism, they turned out to have BPD. Now, imagine if a self-diagnosed autistic who actually has BPD doesn't and/or can't go through a proper ASD assessment (and to an extent isn't aware of their BPD either, because as I said, lack of proper assessment), and they enter the autism community, manifesting their behavior in less than ideal ways, which does more harm and good. This is one possible, and perhaps damaging result of the emergence of self-diagnosis. But at the same time, the system doesn't provide the assessment, and so self-diagnosis is the only pathway to understand what may be wrong with us. The thing we must collectively fight for is to make official diagnosis more accessible and affordible, the methods vary depending on the country, of course.

Full disclosure: I was officially diagnosed as a toddler. But I know many adults who resorted to self-diagnosis or get diagnosed remotely (by people who may or may not be qualified to do such assessment) because assessment for adults is difficult here. The local psychologists have not proven that they use the proper diagnostic tools to assess autistics in adults; a big hurdle is the lack of local translations.