@Jellycats4life i think you’ve missed the point as to what that poster was saying.
There is (IMO) an assumption sometimes that there are basically two camps: one camp is NT and they are ‘normal’; fine, OK.
Then there are those who are ND who, without having a diagnosis explicitly saying they are ND will believe themselves to be (as you put it) weird, unlikeable, failures.
The reality is far, far more nuanced than this with numerous grey spots and crossovers. If we take just a few hypothetical examples from this thread alone, we have young people who are fairly sure (as are their teachers : caregivers) they are ND, but they come from affluent, educated backgrounds, their schools are happy to make adjustments for them, they are confident and happy with who they are. I wouldn’t say they ‘need’ a diagnosis in order to stop them believing negative self thoughts or to give them confidence. They are accepted and supported for who and what they are.
If we imagine a hypothetical NT child, with no autism or ADHD we are aware of but who comes from a chaotic background with numerous house and school moves, no real stability in terms of home environment or friendships, relationships with teachers, and we all know these children do exist, well - they might not have ADHD or autism but they may well grow up with feelings of being a failure, of not fitting in, of self doubt and so on.
In other words, you’ve grown up believing awful things about yourself. Since then, you have realised these things were not true, they were because of autism.
What if someone had turned around and said ‘no, you aren’t autistic.’ Would you have then concluded ‘oh, actually I am just an unlikeable, weird failure’?
And we are all products of our environments - autism / ADHD or not. One of the things I’m hyper aware with re DS is not to be constantly correcting and chipping at him. Sometimes hard not to.
Just as ‘if you’ve met one person with autism, you’ve met one person with autism’ stands that’s true of people generally. There are many odd, difficult NT people and many people who are ND can be charismatic, charming, mask so well that if they are autistic barely anyone would know (I wonder this about myself actually!)