There are certain things I’ve just got to shut up about, like the fact that my colleague crackling her water bottle makes me want to commit murder and my husband putting on Christmas songs at the same time the children are watching TV makes me want to run out of the house screaming!
You don't have to "just shut up" about those things, you can leave the room until the noise stops. You can put on noise-cancelling headphones.
I mask bloody well because what choice do I have?
I have had meltdowns and twice have actually fainted, passed out, because I couldn't mask any more. A person's capacity to mask isn't infinite. Sometimes, failing to mask is inevitable. This "what choice do I have?" argument stokes the narrative that we could all cope with everything if we just tried harder because "needs must".
Some of the things I massively struggle with are just part of life
I recently had a job interview in which I asked for the interview questions in advance and for the panel to book a room with dimmable lights if one was available. Some of the "just part of life" things can be adjusted. I found this out after diagnosis when I started looking at what other autistic people do to help themselves. When you can confidently request an adjustment, knowing that you can email your diagnostic report over to prove the need, it really does make a huge difference.
it would have made me lose confidence and not seek others
It gives me confidence. With a few words, "I was diagnosed as autistic in YEAR", I can convey to people why I come across as a bit odd and filter out jerks. I can spend less mental effort on trying to "act normal" and more on actually trying to engage sincerely with the other person. It acts as a safety net for minor social errors, like thinking someone has finished speaking when they haven't and butting in. I used to stay silent in groups for fear of butting in and being seen as rude, and then of course people still thought I was rude because they perceived me as standoffish and antisocial. Having a diagnosis has literally given me a voice in those situations.
You're an adult saying "well, I cope well enough", and you have the agency as an adult to make that decision. This isn't the same as a parent deciding for a child "well, she copes well enough". Why would any parent want to deny their child that safety net of future support?