> If a UK citizen were to post as offensively as a US citizen they would and have been arrested.
The idea of posting something and being arrested disgusts me. The bar around the world for such an action should be just as high as it is in America. If I post that I'm going to come and kill you, thinkingemote, at 10:17 a.m. at your place of work located at <insert address here>, then by all means I deserve to be arrested. I've made a credible threat with credible information, verified by the fact I know your name and your workplace address.
However, saying something "mean" to you, or "misgendering" you, or even calling you a racial slur, should never be enough to arrest someone.
It reminds me of one of the few (maybe only...) great lines from Ghostbusters 2: "Being miserable and treating other people like dirt is every New Yorker's God-given right!"
So it should be online as well. If you don't like it, you can absent yourself from the platform(s), and in almost every case, if you don't want to do that, you can block the other person.