The top blurb on Fara Dabhoiwala’s new book describes it as a “remarkable global history of free speech”. But it isn’t, and throwing in an interesting chapter on the press in British-occupied India, a tedious one on 18th-century Scandinavian free-speech laws and referring to the French Revolution doesn’t really make it one.

No, it’s a polemical account of the evolution of American first-amendment exceptionalism (which the author, as we shall see, regards as an entirely bad thing), with most of the globe entirely omitted. You suspect the author all the way through of having what Keats called “palpable designs” on you, but you don’t fully catch up with his intentions until towards the end.

I don’t mean by this criticism that there aren’t many interesting things to be discovered in the nearly 500 pages, but the arc of this history is bent towards its conclusion that what has gone before has led to abolishing “any constraint on hateful or otherwise discriminatory speech. Nowadays American Nazis, antisemites, racists and other spreaders of group hatred shelter behind the first amendment. American media companies proudly follow the same principles, and export them around the globe, with predictable results.”

The people who got us there, though often celebrated by less perspicacious historians, were mostly a bad lot. Dabhoiwala traces the popular origin of free-speech absolutism to John Trenchard and Thomas Gordon, two English journalists of the early 18th century (Dabhoiwala’s period), who wrote the principal, crude argument for freedom of the press – that freedom of expression improved society – in a series of pseudonymous letters for a London newspaper in the early 1720s.

But these men were slavers and liars and were prepared to be seduced by powerful men to express entirely contrary opinions for money. Thus setting a standard for western journalism which Dabhoiwala – deploying words such as “venal” and “mercenary” – evidently believes has largely been followed ever since.

Nevertheless they were influential and their ideas were picked up by the American revolutionaries and encoded in many state laws and in the first US constitution. Or, as Dabhoiwala characterises them, “violent rebel settlers deeply distrustful of governmental power and obsessed with individual liberty for propertied white men”. The caveats on free expression developed by the French revolutionaries (their colour unstipulated) concerning public safety were not employed by these violent settlers – an omission that Dabhoiwala seems to consider lamentable despite the fact that, arguably, the French exception led to the guillotine.

Meanwhile there was another twist to be added to the free speech argument. In 1859 John Stuart Mill published On Liberty, in which he maintained that the question was not so much whether free speech improved society, but that it was a right attached to the human being. This Dabhoiwala deprecates for its failure to allow that speech is an action like any other and like any other can cause harm: so logically a right​, so it must be tempered by its effects on others. This is an observation with which the author regularly (and after a while, irritatingly) punctuates the book.

Mill though, is flawed in another way. Being a supporter of British rule in India and possessing a contemporary attitude towards the empire’s subjects, it follows that “his argument was also rooted in a deeply colonialist presumption: that Europeans alone stood in the vanguard of history … [at a] fundamental level, therefore, Mill’s argument about freedom of expression was saturated with imperialist presumptions about history, ‘progress’ and a sharply perceived division between ‘civilised’ Europeans and ‘barbarian’ others”.

Note the quote marks here, because the author makes a lot of use of orphan quotes when he wants to distance himself from his subjects. It’s a bad habit but probably not as bad as judging historical characters by the standards of today. In any case it simply isn’t true that Mill’s idea itself is marked by imperialist attitudes, as Dabhoiwala more or less admits when (in one of the book’s most interesting sections) he talks about how Indians adopted the rhetoric of free speech to gain entry into national discussion.

Bear this double-edged nature of free speech in mind – that sauce for the goose can be (no – will be) sauce for the gander and that what the author calls “libertarian platitudes” have been ideas that have encouraged and assisted generations of dissidents and freethinkers. To him, however, “Since it was first coined, 300 years ago ‘free speech’ [has] been a perennially weaponised slogan, wielded as often by the powerful against the weak as by the weak against the strong.”

Really? I spent five years as chair of the freedom of expression advocacy organisation, Index on Censorship, set up originally to support dissidents in the Soviet Union. In those years we heard among many others from the Angola journalist pursued, imprisoned and almost killed because of his exposure of corruption, from the South African lesbian performer whose shows were disrupted and whose life was threatened, from the Belarusian human rights campaigner who is still in Lukashenko’s prison.

Dabhoiwala writes that “even in the most oppressive circumstances [free speech] remains irrepressible and potentially subversive. It’s not truly possible to stop people from communicating any more than we can stop them from thinking”. That word “truly” is doing some work here. You can pretty much silence most of the people most of the time if you’re prepared to put in the hard, totalitarian yards. Which is why “free speech”, if it is a platitude, is one of the most important that we possess.

So what does Dabhoiwala consider to be the necessary boundaries of free speech? Don’t ask, because, “the real questions are never ‘should people be allowed to say that?’, let alone ‘do you support free speech?’ They are, rather – what should ‘freedom’ mean? What is free speech for? And, whose speech are we talking about, where and to whom?”

This dictum should prevent me from asking whether, say, he thinks Salman Rushdie should have been able to publish The Satanic Verses, or whether this fitted the social harm category of “demeaning a vulnerable immigrant minority” by ridiculing “their holiest beliefs”?

Rushdie does indeed make a cameo appearance, but only as a free speech absolutist who, Dabhoiwala implies, “feels good” by standing against censorship. Rushdie’s persecution at the hands of religious extremists is not even mentioned, doubly remarkable because while the book was being written he was attacked and almost killed 300 miles away from Princeton where Dabhoiwala teaches.

I am not saying that the author does not make many good and valuable points and that he’s entirely wrong to be alarmed at the use that extremists can make of free speech arguments. But even more worrying – as he might see had he written a history of the repression of free expression – is the use that authoritarians of all stripes can make of his own book.

• What Is Free Speech? The History of a Dangerous Idea by Fara Dabhoiwala is published by Allen Lane (£30). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply