[marky1991]

As a us person, I don't even know what deaf-mute means? (Is it deaf and mute? Like Helen Keller?) I've literally never heard the word used in my life.

But I'm sure basically any word has been used as an insult in some context, that doesn't mean it's useful to consider all such usage as such.

[wizzwizz4]

Helen Keller was deaf-blind but not mute: she gave many of the speeches she wrote, although she never got her speech as clear as she would've liked. (See e.g. https://redirect.invidious.io/watch?v=8ch_H8pt9M8&t=124) Despite what the National Association of the Deaf's Community and Culture FAQ claims, deaf people can learn to speak: it's just a lot harder, since they have to approach it as an applied articulatory phonetics exercise. (Helen Keller used the Tadoma method to get information that a sighted deaf person might get visually: https://redirect.invidious.io/watch?v=GzlriQv16gg)

If you're neither a bigot nor a member of a minority group, you're unlikely to be familiar with the slurs used against members of that group. And, of course, different cultures have different slurs. The fact we've never observed these words being used as slurs doesn't mean they aren't predominately used that way, in certain cultures.