We're Not Silencers, We're Silenced Too
As a result, it seems like some parents become very vigilant about making sure their voices are heard, rather than 'experts' who know nothing about their lives dictating what's going on. This is a good thing. It's an adaptive response to being silenced. It means you are advocating for yourself and your child, and both of you stand to benefit from it.
But when these parents meet disabled self-advocates (especially, it seems, when parents of autistics meet autistic self-advocates), too often they don't turn this off. They don't see us as different from professionals in the field of autism. And when we start to say that we need to be heard, rather than just having parents of kids like us talk, and we say things about parents not understanding their children and making mistakes, the parents see it as 'yet another expert come to shut us up and tell us what we're doing wrong'.
And the reaction that is a good and productive thing against the know-it-all professionals who aren't listening to parents gets directed at people trying to speak up about their own lives, and the lives of others like them. People who are even more silenced than parents of disabled kids, whose voices are less often heard. And these advocate parents end up reinforcing and perpetuating oppression against their own children.
What parents need to remember is that just because you are the one being silenced and treated unfairly when talking to professionals, doesn't mean that's true in other circumstances. You can be the perpetrator of oppression in one setting, even though you're the victim of it in another setting. Parents need to remember that fighting back against oppression can seem to the priviledged ones like oppressing them, and that you can be more priviledged than another group even though you're part of an oppressed group too.
And most importantly, parents need to remember who and what they are fighting for. They are fighting for their children. And we, (in the group sense) are their children. Parents should imagine their child, grown up and able to speak or type their self-advocacy, talking to other parents about what they want for children like them. Would you want those parents to reply the way you have?