> The US's first amendment is rather unique amongst Western nations.
> As far as I know, this kind of language is absent from other Western nations. For example, Canada jails people for criticizing those of Islamic persuasion.
The US is not unique in having constitutional protections of free speech. For example part of the Canadian constitution is the "Canadian Charter of Rights and Freedoms", which forms part of the Constitution Act 1982. Section 2 of which says "Everyone has the following fundamental freedoms: (a) freedom of conscience and religion; (b) freedom of thought, belief, opinion and expression, including freedom of the press and other media of communication;" – that's essentially saying the same thing as the US First Amendment.
In Europe, article 9 of the European Convention on Human Rights (ECHR) protects "Freedom of thought, conscience and religion". The Convention is quasi-constitutional in nature – while it is an international treaty whose members are in theory free to leave at any time, in practice quitting it is impossible for many European countries–membership in the ECHR is a requirement for EU membership, so no EU country is going to get away with denouncing it. And many national constitutions have equivalent provisions, such as articles 4 and 5 of the Basic Law of Germany.
One difference – the text of the US constitution doesn't contain any exceptions to the 1st Amendment, whereas the Canadian constitution, the ECHR, Germany's Basic Law, etc, explicitly state that freedom of speech/etc can be subject to limitations. However, in practice, even though the US constitution never explicitly says that the 1st Amendment has exceptions, the Supreme Court has always held that it does, although the scope of these exceptions has varied due to the evolving opinions of the Supreme Court – for the first century of the US's existence, SCOTUS allowed sweeping exceptions to the 1st Amendment; in the 20th century, it narrowed the allowed exceptions significantly, and developed some highly complex case law on which exceptions are allowed.
The real difference is actually nothing to do with the text itself, it is all about case law – since the 20th century, SCOTUS has been very strict in only allowing quite limited exceptions to the 1st Amendment. Courts in Canada, Europe, etc, have always been much more liberal in allowing exceptions to the right of free speech. Now, possibly the difference between a text which provides no explicit exceptions versus a text which does may have influenced that, but I don't think it was decisive. It was not historically inevitable that SCOTUS would start interpreting the 1st Amendment much more strictly in the 20th century, if different justices had been appointed, it easily could have decided to stick with its 19th century case law which allowed greater exceptions to it. Conversely, even though Canadian/European/etc texts explicitly mention exceptions, their courts could have chosen to interpret those explicit exceptions far more narrowly, producing a result much closer to that of the US, if they had wished to do so.