@Coronawireless
There's a big difference between 'I speak for everyone else', and 'sorry, but you don't speak for me'.
It happens both ways in practically every mumsnet thread about Autism.
Something that occurs regularly here, is someone will start a thread describing what they interpret to be an 'autistic' behaviour, or the behaviour of an individual that they suspect might be undiagnosed. There's a cacophony of indignant responses along the lines of 'how dare you, we're not all the same/none of these things are typical in autism/that's not an autistic person, they're just an arsehole'. Meanwhile, I'm looking at the OP and recognising that they've described me, with my diagnosis, to a tee.
People are perfectly entitled to own their own diagnosis, to describe it as they see fit, to describe themselves as they see fit, including taking ownership of and embracing terms other people might find offensive, and/or disagree with other people's interpretations and views. There's no 'right' or 'wrong', and it's not dogmatic to express a view on what you personally feel or believe about your own diagnosis and how it's often portrayed or described by others.
Frankly, I think it's far more important to emphasise that people with autism are every bit as diverse and unique as NT people, than it is to argue over labels and terms, but it's still perfectly ok to have a debate about labels and terms and discuss why you might find them objectionable, inappropriate, unhelpful, necessary, or unnecessary. I don't think any of that amounts to anyone attempting to 'speak for everyone else'.
If other people find that the term that best describes for their situation is 'High/Low Functioning', then great, continue to use it by all means. I won't, because it's insufficient to serve any worthwhile purpose for me on a personal level, but I can still understand what someone might mean when they use the term. Likewise, I won't accept being forced to use those terms about myself, and I happily take ownership of other terms, many of which are widely regarded as offensive, because I'm applying them situationally to myself and in close company that I know understands my humour and my intent behind their use.