Let's clear this up...
When I say I am "Autistic":

I use "autistic" as a general term for the entire autism spectrum. I think Asperger's and other types of autism are too similar, with too much overlap between them and no clear dividing line, with too many cases on the borderline between them, to be truly separate entities. Certainly you can pick examples of other types of autism that are very far away from certain other examples of Asperger's, but you can also pick examples where they are entirely indistinguishable. I am more in favor of a broad range of expressions of Autism than separate entities with different names. When I say I am "autistic", I am saying I am "on the autism spectrum", not that my official diagnosis has suddenly switched from Asperger's Disorder to Autistic Disorder (it hasn't, and there's been no reason to re-classify, since one is as good as the other and it gets me the services I need).

The way the ASDs are diagnosed, the names have become pretty close to meaningless. There's the whole annoying problem of the diagnostic criteria overlapping to the point that most Asperger's cases, including mine, can also be diagnosed as Autistic Disorder. Diagnosis is often based entirely on what the doctor thinks will get the child the proper services, or the doctor's impression of functioning level (which doesn't actually even have an official definition), or even an attempt not to say "autism" and diagnose PDD-NOS in a person who clearly fits into the Autistic Disorder category.

The only diagnostic sure thing I know of is that someone who is labeled Asperger's generally has some use of spoken language, though whether it's reliable or whether it was delayed is anyone's guess. They don't diagnose by-the-book, so the labels don't mean too much; and if they did diagnose by the book, the labels still wouldn't mean very much because the Autistic Disorder category would pick up so many more cases from the PDD-NOS and Asperger's groups.

In any one ASD category, you'll have wildly different people with the same label. Pick one person diagnosed Asperger's, and you might have a shy bookworm with a PhD; pick another one, and you might come up with a wildly eccentric extrovert who repeatedly embarrasses himself and doesn't care; pick a third, and you might have an overly polite housewife who doesn't get out much and spends a lot of time on the Internet. For that matter, you could pick the same three people out of the "Autistic Disorder" or "PDD-NOS" boxes.

If you can't predict what someone will be like based on the particular ASD they have, and if you can't predict what particular ASD they will be diagnosed with based on what they are like, then aren't the specific categories a bit meaningless to begin with?

So I have decided to forgo identifying as any precise diagnosis and simply gone for calling myself "autistic". This is the general term for anyone with a PDD--Autistic Disorder, Asperger's, Rett's, CDD, and PDD-NOS--and I much prefer it to compartmentalizing the spectrum artificially, especially since I have grown very annoyed with the tendency to say one group is either "better off" or "more truly autistic" than another. There's too much divide-and-conquer going on as it is; until there are better official criteria, I'm going to forget about specific labels altogether.

We're just going to have to deal with the fact that we are too diverse for any one way of experiencing autism to be anything near universal; and we're better off wasting no time making it clear that human rights apply no matter what sort of weird brain you have. Who says you can't demand universal human rights for people who don't experience autism the same way you do?

No, you don't know "what it's like" to be someone else. No, you can't speak for them any more than you could speak for your identically autistic twin. (Those who think we share an "autistic hive mind" are sadly mistaken and should see us argue some time!) Of course you can't; you can't move into someone else's brain and know what they are thinking! Besides, a lot of what this neurodiversity thing is all about is that everybody gets to speak for himself. That, and actually being represented by people who are autistic, not NT psychologists, which is about as silly as having somebody who's lived all his life in Canada represent the interests of people in Madagascar.

Bottom line: Despite all the diversity, there's no reason we shouldn't work together. After all, the only thing you really need to demand human rights for someone else is to be as human as they are. Last I heard, we all had that in common.