Why is “retard” now considered offensive to people with intellectual disabilities?

Let's get myself banned while we're at it. This site is boring now. But I don't see how someone can say 'retard' is so offensive to learning-disabled people when I grew up in the 80s and my learning-disabled friends used that word too. And we weren't directing it to people when we said, "That movie was retarded."

The word has Latin origins long predating mental illness. It meant to "hinder, delay" as we use for "paint retarder" and "fire retardant". I never used this word to mean ill for mentally disabled people. Suddenly it's like I'm a KKK Imperial Wizard because I said, "That idea is retarded."

I don't understand how we're suppose to sustain all these changes in society. "Men can get pregnant too." Me: "How's that supposed to be sustainable?" I'm totally cool with calling a transwoman a "she" and transman a "he" but "men can get pregnant too" is a lot all a sudden. How am I supposed to read Shakespeare now? Or take "Latinx" and "Amigue" for Spanish speakers.

We're just supposed to adapt to this now when all our books, movies, our entire history, doesn't operate like this? We just throw a million dependencies way to this legacy code? In my experience as a software engineer, that is a recipe for failure.

So anyway, more of a rant than a Q. Since we can't even do MyTakes now. But why's 'retard' supposed to be offensive all of a sudden, and how do you think it improves society to deem it so in a world of the entirety of English speakers, including ones like me who learned English starting in Japan?

Updates
6 h
For people who think this word is so offensive all of a sudden, would you put Mike Judge up there making cartoons and movies up there with a hate monger? What is a Japanese teenager supposed to think when they watch "Beavis & Butthead" and hear that word? And what are you aiming to do about it if they think it's okay to use this word on the internet?
Updates
6 h
Shouldn't intention and malice be the driving force of what is truly offensive in a globally-connected society? It should be offensive to call even a learning disabled person an "idiot" or a person who can't speak "dumb". I will stand beside those and call those bullying them an "asshole". But it doesn't make sense to me to pick on people saying, "That movie was retarded."
Why is “retard” now considered offensive to people with intellectual disabilities?
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