Ok, I've finished having a huge mental overload and can actually think, so here goes.
I'm not saying either of them is worth more.
I'm saying it's about whether you know better. That is what makes acting like either of them wrong when a non disabled adult does it.
To stick with the pooping example...when the handicapped person, or indeed kid, does it, it's no reflection on them because they don't know better. If I do it as a 21 year old woman with a normal IQ, it is a reflection on me because I know better.