Offence is meaningless. White people are occasionally offended by 'cracker', rich people by other terms, but they don't cause material harm to them. But people of colour are hurt by words like 'n$@!%r".
Words themselves have no meaning. The meaning is derived by the intention and context. It is perfectly correct to use nigger in some context. Just look at Louis CK or George Carlin. Actually George Carlin made a bit about the word nigger and he made pretty good arguments against the American obsession with "bad" words. The Americans have a very childish attitude towards this, I haven't seen any country were adults refer to words by their first letter.
As if somehow euphemism make everything ok, even though you say 'n$@!%r", you are still saying nigger.
Linguist here: you haven't seen much, this "obsession" is inherent to language itself and has a name of its own: connotation. Connotation is everything associated with a word, denotation is what the word actually means. But denotation doesn't override connotation, they coexist. If anything, connotation can change denotation, while connotation changes independently from denotation.
So what's the difference between saying nigger and meaning nigger? When you're saying nigger, you give away the option of not meaning nigger, because you cannot use the word free of its connotation: it's there, no matter how you use it. Dogwhistle terms used instead of nigger do not have that universal connotation to them, which is precisely why they are used: they can slip under the radar.
So what to do? Honestly, this is extremely simple: don't say nigger if you don't want people to equate what you're saying with the connotation your words carry. And the same goes for retard: if you don't want people to equate your words with the hate directed at people with mental health issues, don't use words whose connotation is limited to that hate. The denotation of "Sieg Heil" is completely harmless, but you have no problem with understanding its connotation and you don't go around saying it when the denotation fits because you know that only Nazis say "Sieg Heil".
Well, only assholes say retarded or retard. That's the connotation you're associating yourself with and no matter how much you complain about being misunderstood and people being too PC, you just messed up by not paying attention to the connotation of the word.
Oh, so when someone calls me a totally racist and offensive slur against white people it causes no harm, but when white people call blacks what they call each other all the time it hurts them... definitely makes sense.
Anyway as a git I am offended by the use of the word git and it makes it hard for me to participate in such spaces.