The vast majority of folks who self diagnose are looking for answers and context to why they act and feel as they do. They aren't looking for a documented excuse for poor or outrageous behaviour. Monetary fraud associated with faking a diagnosis of ASD1 are almost laughably small in the US.
Those who do decide to self diagnose and portray 'autism' also usually aren't bringing just an ASD1 diagnosis to the table, usually there is an entire legion of additional and c-ooccuring conditions, e.g. fibromyalgia, anxiety, deprssion, EDS, gastrointestinal involvement, etc.
Boldened areas by me.
I am self diagnosed as Level 1 autistic and deciding whether to get a formal diagnosis. It has been life-changing to find out that I am ASD; it explained my sensory issues, social difficulties, meltdowns and shutdowns. It also saved my marriage. When both partners realize that one of them has ASD, it provides an explanation of what is happening and how to properly address it. Changes in the environment, in communication, in scheduling, etc are made that allow both partners to exist in (more) harmony. And it opens up a whole new world to the partner with ASD; I never realized that there is this big broader world of emotion out there; emotional communication, emotional intelligence, emotional reciprocity. I never knew these things existed anywhere near to the extent that they do. I consider the realm of emotions to be nebulous and engulfing and scary. I have alexithymia and have to work at it. I am also a woman on the spectrum.
Example of the realm of emotions in relationships: Do not interpret what the spouse says literally; he may not mean it literally. There is usually an underlying emotional message behind what he is saying. Responding only to the literal word message, and not the hidden emotional message, will lead to marital conflict. I had to learn about that--still learning.
Oh and also, apparently getting a formal diagnosis costs $1,000 to $7,000, so that is a significant barrier to an official diagnosis. In many cases, all you can do, or all you need to do, is self-diagnose.
And you're right about co-occurring conditions. I also have Celiac Disease (confirmed by blood test, not self-diagnosed), and food sensitivities (no reliable test for those yet though).