This is kind of a draft for a comment I want to write somewhere, but might end up not posting if I can't get it out right.
Basically, I see a lot of people talking about the TPGA dialogues as a situation when parents and self-advocates were both focused on the issues that personally affected them and didn't want to listen to the other side or didn't want to compromise.
As a person with a disability, I'd just like to say: I love parents. They're totally sweet. I read some parent blogs that I really like and that are helpful to me in thinking about anti-ableism more broadly (since most of the disabled people I meet on the Internet have certain abilities by definition). But this doesn't have much to do with the reasons a lot of Autistic people on the TPGA threads were saying things that made parents feel "uncomfortable" and "silenced."
I think it comes down to the fact that a lot of the Autistic people who were in the conversation are involved in the kind of Internet social justice atmosphere where the concept of privilege is very central. The article I linked to probably isn't the best explanation of privilege, but it is hard to find one article or blog post that explains it really well. But basically privilege refers to the benefits that someone has when they don't belong to an oppressed group. For example I have white privilege and class privilege (and a lot of other kinds of privilege).
A really important aspect of privilege is that a lot of people who have it may not realize that they have it or how much and this can lead to a tendency to center their own experience because they don't realize how much their experience is already centered. That tendency can take the form of feeling like something is being taken away from them when in fact a situation is being made more equal. (I'm not trying to attack anyone by saying this, I just want to explain the concept.)
Where I went to college, there was a fairly big community of students who either were trans or cared a lot about being supportive of people who were trans. In almost every student group and even occasionally in classes, it had become the norm to ask people to state their preferred pronoun when introducing themselves. This can make things easier for someone who is often perceived as a different gender from what they actually are, since they can address potential misunderstandings before they happen.
Sometimes you would hear people who were not trans, who were very nice people, saying things like, "I hate going around the room and saying pronouns. Like, 'I'm sorry I'm not special!'" Because they had never had to tell people what their gender was, they found it a silly thing to do at best, and at worst, they actually felt that they looked boring and "not special" when they asked for the pronoun that would probably already have been used for them. Even though their boring and "not special" answer was being given by most of the people in the room.
I've also seen a lot of non-trans people feel like they are being insulted when they are called the word "cis," which is just a synonym for non-trans. The word NT, while not one I especially like, doesn't need to be branded a slur by people without disabilities, but I have definitely seen them have that reaction. In both examples, people from the dominant group seem offended by the idea of being called any word at all, instead of just being the group that is nameless because everyone is assumed to belong to it.
I think you might be getting to see why this seems like too long and involved a comment to post on the blog of someone I don't know! But to return to the TPGA dialogues, it is believed in the social justice community (by social justice I mean a certain way of looking at the world) that the appropriate way to talk about oppression is for the people who don't have privilege to be the authority because they experience the oppression firsthand. This doesn't mean that people who are privileged shouldn't get to talk at all, but that if a lot of oppressed people are saying a particular thing about oppression, the privileged people should accept it is true, even if it means apologizing for something they did wrong.
Also, to reiterate, since privileged people often feel attacked just because a situation is being made more equal, someone who thinks about social justice this way is probably not going to feel guilty and back off just because a privileged person says, "I feel like I'm being silenced and people from my group aren't allowed to talk." In fact, the reaction is more likely to be, "What you feel isn't the point."
If a parent thinks that the problem with TPGA dialogues has to do with, for example, everyone only caring about how anti-ableism could personally help them, then I don't think they understand what happened. It isn't possible to understand a lot of the things said by people with disabilities if you don't, either academically or just personally, understand the concept of privilege.