I love the USA and many of my heroes, artistic and otherwise, are American. I know that sounds like the suspect "some of my best friends" defence and preamble, but it is true and I spend a lot of my life enjoying all that music, literature and culture.
But I do sometimes feel the need to resist US domination of the English-speaking media, especially the Twittersphere. Resentment can bubble up, like those clouds on the weather forecast, with thoughts about cultural imperialism and even about the "can do" attitude. This positive, but often combative, approach is admirable in many ways, I'm sure. But, don't you sometimes think, "Oh, why can't they leave well alone?" rather than their saying, "We can fix it, zap it with something." I think I am peeved this week because the BBC News style guide website has just adopted what seems to me yet another AmE usage.
Consider the long-running #WhichvsThat debate - yes, it has its own Twitter hashtag. Journalists and lawyers, for example, may sometimes have problems with punctuation, especially if they are under pressure. (Perhaps also with relative clauses, but it is less a question of that, I feel.) The solution in the US media - and the UK always seems to follow nowadays - seems to be zap the difficulties on this point by instituting a clear, prescriptive (and proscriptive) rule, at least in usage and style guides: "That defines and which adds information" or something similar. I suppose it might seem to simplify things if you have an urgent deadline.
The problem with simplifying and then blasting problems is that this may seem to help in that moment but it leads to other difficulties you haven't thought of. ("Unknown unknowns"? What great philosopher said that?) In this case you might think you have dealt with it and so don't have to worry about it any more (anymore? No, not yet!). The "guidance" might help you write faster but probably reduces the likelihood of your reading the sentence aloud, or even internally.
In fact, that is all the problem comes down to. Do you read with a pause, to add extra information (comma needed) or read on in one phrase (no comma, defining)? It is not really a choice between
"which" and "that" at all. "Which" is fine as long as you know what you mean. "That" isn't, but if
your English is good it should come naturally.
The trouble is (is is) that even "wordsmiths" seem to be losing what used to be called their "native speaker performance/competence" - my double or treble is is another example. This may be a result of both the huge volume of unedited language, much of it from admired or, at least, celebrity figures, available on all sorts of media. But also, strangely, partly as the result of "rules" which seem to be authoritative but are simply made up for convenience, against the feel and sounds and even instincts of the English language.