Getting a diagnosis can be extremely difficult for people. In my area you either need to pay about $5k or go through a 2+ year ordeal.
Even with all that, diagnostic methods are murky at best. There is no binary you have it or you don't kind of thing, no physical test that can conclusively say you are autistic.
All that to say as someone who went through the process to get diagnosed. I think self diagnosis is perfectly valid with autism.