I don't think so.
First of all bastion is simply an old Italian world for fortress, which means fortified place, which means
a stronghold.
Definition of bastion - Merriam-Webster Online Dictionary. It was, metaphorically, supposed to mean exactly that - Boston had a forceful organization of deaf pple.
let's analyze:
We were living in Boston at the time, which was a bastion of Deaf culture.
In the first part it is said the place where they were living (Boston) was - a second part - a bastion of deaf culture.
meaning - she said they were living in a city that had a strong deaf culture going on,
BUT
oral programs were not plentiful,
BUT - the ORAL services they had on offer were not to their satisfaction, and they (the parents)
but we very much wanted Rachel to be able to take advantage of all the opportunities the hearing world had to offer.
they wanted Rachel to be able to hear and speak as well as possible.
Since the programs they wanted were not available, they opted to go oral only.
BUT still -
"we still had time to turn to sign if it didn't work."
they kept in mind this might not work, and
evaluated that if their oral approach fails, they still will be time for sign. (meaning, they knew about time passing for learning to sign, and decided there is sufficient time)
So no they weren't using "bastion" in negative way.
They just said Boston had a strong deaf community.
Fuzzy