The US Supreme Court has ruled that the First Amendment is consistent with several arguably reasonable limits on free expression, including:
* Expression that incites criminal action;
* Expression that causes injury;
* Obscenity via the Miller Test;
* Child pornography;
* Regulation of commercial speech;
* Copyright and other 'intellectual property' restrictions;
and so on.
Of course, the various other liberal democracies also enshrine the right to free expression; and they also enforce arguably reasonable limits on that right, some of which are similar to the limits in the US and some of which are slightly different.
Is a country where you can be fined for saying "fuck" on television more or less free than a country where you can be fined for saying a minority should be exterminated, where it can be shown that hateful propaganda has the effect of silencing a whole group of people?
There is nothing special about the US Constitution. It is no better, and in many ways worse, than the constitutions of other liberal democracies. The US Constitution is a legal, historical document that admits of many possible interpretations, and it is nothing if not misleading to pretend to absolutism, however selective, in how it shapes the law.
As for the Second Amendment, the US is perhaps the only liberal democracy that perceives a need to guarantee a citizen's right to own and bear firearms, based on the 18th century idea that governments are inherently tyrannical and the only way to guarantee liberty is with the constant threat of violent rebellion.
As we have seen, this belief has been disproven. The citizens of other countries are able to keep their governments more or less honest through maintaining formal and informal democratic institutions and civic engagement - indeed, the governments of many other countries are more responsive and accountable to their citizens than the US government.