That ship has sailed, unfortunately. On social media where no markup is permitted (or possible), people will use these to stand out — especially those who make money on those platforms (not much of a problem on Mastodon though). We, the people who know how this works, can explain all we want, but it will always sound like a hypothetical edge case, even though this does exclude some people from participating.

The only way to stop this would to be to have the platforms where this is abused prevent its use (which would harm legitimate use too, although that is not nearly as prevalent as the 'I just want bold and italic'-case), have those platforms introduce minimal markup (not necessarily wanted), or have browsers and screen readers support these characters (not trivial, I suspect).