One of the few principles of the 18th Century Enlightenment that will be familiar to many people today is that of Voltaire:
It is a principle for which many Britons have indeed died, when Conservatives and Communists, Empire Loyalists and Anarchists, jointly fought against those who challenged such an important part of who we are as a nation.
And then along came Jacqui Smith.
American "Shock Jock" Michael Savage has been excluded from entry to this country. He had no plans to come here. He poses no threat to any person here, and yet has been placed in the same category of persons as Russian Nazi Skinheads who promote the attacking of Jews and those who promote suicide bombing. Why?
If the Conservative Party is to establish itself as a true defender of liberty it is essential that this simple question is asked, pursued, and driven home between now and the coming election as a litmus test of whether this country is to be a truly liberal society – in the true sense of the word – or an increasingly narrow one where debate can be restricted in accordance with an increasingly narrow "progressively radical" agenda.
Mr Savage will not be to everyone's taste, even in the Conservative Party. He expresses himself in forthright terms.
He dislikes the influence of the Hollywood "gay mafia" in a similar way that climate change protesters "hate" Big Oil. He asks liberal priests where in the Bible it says it is OK to kill children in the womb. Strong stuff, discomforting to many perhaps, but surely not something that has yet become un-sayable in a free society?
He does not, however, promote "hatred" in a way that places him in a different category than, say, Michael Moore, who could, to no greater or lesser degree, have been said to have promoted "hatred" of George W Bush".
I strongly suspect that in accordance with its "balanced" approach, the Government dare not ban an Islamic figure without finding someone from a different perspective to "prove" its even-handedness. That is the signifier of their moral cowardice.
If Mr Savage does not want to come here, it would be easy to let this matter pass, and yet the fundamental question surely divides who we are, from who New Labour has become. It is a cause that is still capable of rousing the libertarian instincts in all parts of society, those who agree with Mr Savage and those who do not.
It is a simple but important watershed moment and if we deserve to be trusted with shaping the future of our country in accordance with the finest traditions of the past it is essential that we do not fail the test.
The country that could accommodate Karl Marx can surely cope with a Californian polemicist like Mr Savage.