I was listening on the radio recently to a director who had been accused of this "ableism" in a film she had directed about a young woman with autism, where the character was played by an NT actress.
The director argued that she had originally cast a woman with autism, who then was too anxious and overwhelmed by the whole process day to day to be able to do the job; so she employed an NT actress instead.
I think there are lots of aspects to look at here. A lot of autistic actors have spent their careers playing neurotyoicals; Dan Ackroyd, Daryl Hannah, Paddy Considine are the first three that come to mind. Things like autism can absolutely be played both ways.
But It would be disappointing for a quality aspiring differently abled actor to constantly be overlooked for roles in favour of regularly abled actors pretending to be disabled.
But equally, I don't think that any minority group should be the exclusive preserve of an actor from that minority. For instance, should only trans actors be allowed to play trans characters? Maybe, but the reality is, this is a money game; a well know actor is going to sell the movie to the public more than an unknown trans actor. All that will happen is that big studios will be put off from telling those trans stories by the lack of money making potential in them. Who actually benefits from that?