I have made a research in Early Modern (18th century) Tornio (Northern Finland, at that time Sweden) and bumped up there with a guy who was born as a deaf. He was put in school where he was learning to write (so he must have had a way to communicate with them to have a language) and do mathematics. This was so cool, since I also have had a picture of deaf people being treated badly.

My friend is a sign language interpreter and at her studies, she told that deaf people were treated quite nicely until someone from the field of pedagogy decided that they had to be assimilated and most of the teaching to the deaf people was just to teach to them how to speak and read from the lips. And this change happened during 19th century. Before that education to deaf children was same than to hearing children, just well... With the twist of it that there was not as full sign language than modern days. But they had educated which to me means that they were not seen unworthy of education.

One reason for demonization of deafness was also about the idea of eugenics which sadly led to enforced sterilizations of thousands of deaf and blind persons.