A terrorist speaking in an encoded message to cause wilful harm is still liable for it, even if the words don't exactly say that.
Language is all about context.
If we were so strict about language, most Americans wouldn't qualify to graduate 3rd grade for their botched up spelling of British English.
Your analogy would hold only if people with mental disabilities started trying to reclaim the discriminatory connotations of the word by using it to describe themselves.
And context here is people picked the terms for 4chan-humour value, and it's quite hard to argue non-autists lolling about how an instance of their behaviour is a bit like an autistic stereotype, or hehe trader is an anagram of how uninformed we think these trades are is an obvious candidate for the meaning being completely unrelated to the use of autist and retard as terms of abuse. Same as if I decide to categorise my friends using derivations of a four letter word: I'm doing so because it's a four letter word, and I don't get to play the 'but I meant it affectionately, specifically and non-literally' card if someone asks me not to swear in this establishment
I certainly don't think it's necessary for Discord to ban them, but if your jargon is chosen for edginess, you don't get to act surprised if someone decides it's too edgy.
This should be true, but recent events may prove it false.
What I want to say is that just like there's a huge difference in meaning between "this is shit" and "this is the shit", even usually insulting words can be used in inoffensive ways(like it's done on WSB) - and of course the other way around you can call someone a "genius" and make it obvious you meant the exact opposite.
Language is an incredibly flexible tool and every dictionary definition or scientific description is an obsolete snapshot at best.
what exactly are you basing this "fact" on?
This is becoming increasingly common in discourse these days, and noticing it is the key to understanding the various non sequiturs and other abuses of logic made in arguments that try to classify random stuff as offensive. Unlike in the physical world, in the social world, if enough people are forcefully claiming something is a fact, it becomes a fact.
That's why it's even more important socially to combat such abuse of reasoning than it is in hard sciences. You can't make gravity disappear because you really believe humans are capable of levitating. But you absolutely can make acceptance, due process and individual freedoms disappear if enough people strongly insist some other people are saying the wrong things.
It's a very convenient excuse for banning a controversial community, though. With the sea change we just had in corporate censorship, no one should be surprised.
I hope we get plausible alternatives with a more principled stand towards censorship.
As others have pointed out, "retard" is an anagram of "trader".