Okay, so I know lots of people try to make person first language about not making a person their disability and while that might work for some parts of the disabled community, that is DEFINITELY not the case for most of the autistic community. There are reasons for this, that are pretty self explanatory.

1. Person first language separates a person from autism

This is just scientifically incorrect. You can't separate an autistic person into person and autism. I will discribe this one of two ways. One: An autistic brain is a different operating system. It's not an allistic (not autistic) system with and error. It's a whole different thing. This means we see the world entirely different. We see with autistic eyes, we dream autistic dreams, we hear with autistic ears. There is not a place or aspect where autism ends and you begin. Two: I had it explained to me by another autistic like this. They said 'I'm autistic, I have heart arrhythmia. Autistic is who I am, heart arrhythmia is what I have.' If you gave that person a new heart, they would wake up and be the same person they always were. If you have them a new brain that wasn't autistic, they would not be the same person at all. 

2. It suggests that even when people realize that you can't separate a person from autism, that autism is not central part of who they are. Again, EVERYTHING, and I mean everything about my perception is different from that of an allistic person (get used to allistic, I will being using it a lot).

3. Ingnoring the previous, important, reasons to say autistic person equates being autistic as not worthy of personhood without explicitly stating they're a person. Autistic individuals are people so if your treating them as such that shouldn't need to be stated. This is why a lot of the community often shortens autistic person to just autistic. 

Anyway, I hope you learned something and if you want to know more please check out videos made on YouTube by autistic creators Kaelynn Partlo, Paige Layle, and Chloe Hayden.  Credit to Kaelynn on how the points are organized and how the second and third point are worded.