Not voting for him is one thing, but also being eligible to vote and not voting for Kamala makes one an accomplice too. Even voting for a third party doesn’t count, because that took away votes that could have gone towards the one contender.

Nothing has changed for US users either. Not yet, anyway

Retarded was, and still is, used as an insult for those who are severally developmentally disabled. Those who are literally unable to defend themselves. The people most impacted by this have no ability to take the power back for themselves. You suggest they knew what it meant, but quite frankly I doubt, also having been involved with those with down syndrome. They might have had an idea, but it’s unlikely they all understood all the depths and nuances. And regardless of just down syndrome, there are those with more severe cognitive dysfunction, potentially nonverbal, that literally have no way have reclaiming the word. I don’t think it will become increasingly acceptable, I think it will become increasingly unacceptable.

The other terms you used, while they used to be medical terms, weren’t use in the same connotation to target developmentally disabled individuals. That’s the difference.