Earlier quoted context omitted.
I'm imagining a nightmare scenario where, by some vauge unwritten and immature consensus mechanism, we rationalize even a slight amount of censorship as being OK.
The actual nightmare scenario is that people with learning disability are killed by doctors because those doctors think "retards have no quality of life". When people toss around the word retard they contribute to a culture that doesn't care about the high levels of violent hate crime experienced by people with a learning disability. And most posts seem to miss the point: their servers, their rules. No one is stoppin…
I'm sorry, but this is ridiculous. It simply isn't how language works, never mind political change.
Simple example: "sinister" used to mean left-handed, and by extension, creepy and evil (as was believed by the superstitious in earlier times). Now it no longer means left-handed, but still means creepy and evil. The connotational meaning has become a denotational meaning, because the idea the word used to express is to all intents and purposes gone. Nobody believes such nonsense about left-handed people any more.
Mutatis mutandis, the abolitionists and later civil rights movement did not achieve their aims with regards to racial equality by harassing people for using n-bombs. They fought to change the structural, social reality (slavery, political disenfranchisement, lynchings) that supported the use of such epithets, using all manner of means, from civil disobedience to total war. They had success, albeit not total success.
The idea that you can affect the actual levers of power and privilege in society by imposing overweening social taboos on particular words is a peculiarly modern political disease.
I am not terrifically concerned about whether you can use the word 'retard' on github without incurring the wrath of moderators. (And really guys - github is your resume, I hear. Don't cover it with playground insults.) But it pains me to see plenty of people with some kind of social conscience completely wasting their energy complaining about stuff like this. You want to protect people with mental disabilities? I'm sure there's a state legislature or equivalent near you slashing funds for learning support in schools, or social care, or disability-related welfare benefits (and if it's anything like it is here in the UK, loudmouthed bigots in the press explicitly calling various needy social categories parasites). Cleaning up a github readme is not an adequate substitute.