A group defined by a physical difference becomes a culture when its members share a natural language, a common history, ideas and practices, passed down across generations. For deaf people, sign language is the core of that commonality, turning a medical condition into a shared way of life.
When the majority mistakes a minority's language for mere gestures rather than a real language, it feels justified in banning it. Generations of deaf children were sent to schools that forbade signing and insisted on speech, damage that shaped their lives long afterward.
The gap between how a group sees itself and how the majority sees it shows up in the group's own stories, jokes, and origin tales. These tales spell out which traits members believe they need to exist and survive.
A long experience of intolerance from outsiders leads a minority culture to stay closed, even to sympathetic visitors. Its inner life becomes visible mainly when its own members choose to explain it from the inside.