This is hardly the persuasive argument you think it is.
Yes, the rules are arbitrary. All rules are, when you get right down to it, arbitrary. No rule made by humans is an objective fact or an intrinsic part of the universe.
I’m actually familiar with Pinker. Why? Because I want to learn more about how the English language works, and the bizarre rules that were invented as part of its construction. You might think rules are arbitrary, and therefore supposed to be broken by anyone who is going to commit pen to page, but language is a construct of rules. It’s a sophisticated thing that is built around a structure that enables communication. It’s why, for example, that when you are learning a new language, you learn the base elements of structure - gendered words in French or Spanish, Japanese sentence construction, etc.
See, if I had to sum up Pinker, it wouldn’t be as someone who encourages people to forsake the rules like some kind of anarchist. A lot of what Pinker says comes down to not being worried about the rules if you are constructing a beautiful sentence with them. I’m sure that if you picked any book of a shelf, you would find any number traditional rules of English broken on any page.
In fact, I’ll even point out some advice from Pinker.
“When [James Joyce] wrote long passages with no punctuation and very loose grammar, he was actually trying to achieve an effect. Namely, peek into someone’s consciousness. So, he knew what he was doing. He was flouting those rules for a reason. Ordinarily though, if you’re not trying to render the stream of consciousness, if you’re doing something more like ‘classic style,’ mainly, using conversation to direct the reader’s gaze, then readers have certain expectations about how the grammar works. They do change over time but, at a given time, you can look up what they are and if you ignore them you will often make your prose more ambiguous, you’ll often just confess to your readers, ‘I haven’t paid attention to the printed page in the past.’ You’ll often confess, ‘I don’t think about what my words mean.’ So, for example, if you use literally to mean figuratively. If you say, ‘I literally exploded.’ What you’re saying is, ‘I don’t really care what my words mean,’ and your readers are less likely to trust you. So, I think there are reasons to take care in your choice of words. This doesn’t mean that every rule you remember from your second grade class is a legitimate rule. Many of them are bogus.”
Emphasis mine.