I'm not so sure that Voltaire actually used those words but I am sure that he never defended to the death anyone's right to disagree with him. Like most philosophes of his age and like most so-called enlightened thinkers thereafter, Voltaire was extremely intolerant of those with whom he disagreed. He regarded the Catholic Church in France with contempt and repeatedly called for its destruction. He called it the "infame" and believed it was the cause of most of the problems of pre-Revolutionary France. I believe that the "enlightened" Voltaire was also an anti-Semite.
Another Wall Street Journal columnist, Bret Stephens, also regarded the modern age ushered in by the Enlightenment as a golden age of free speech and tolerance. In a brief sentence he characterized the preceding 2000 years as an era of ignorance and superstition where progressive thinkers were put to death for blasphemy. That period began with the death of Socrates around 400 B.C. and lasted until the execution of Giordano Bruno around 1600.
I know that this incredibly ignorant statement is very popular and that it is even taken as axiomatic in most colleges and universities today. I will not bother to refute its historical inaccuracy here, but will just point out that the modern era has not been a good example of freedom of speech or intellectual inquiry.
From the time of the French Revolution that thinkers like Voltaire helped bring about to the Communist and Fascist revolutions of our own time, freedom of speech has been a victim of fanatical zealots out to suppress all contrary opinions. Maybe these so-called enemies of the State have not been persecuted for blasphemy but they still have been persecuted. I am not speaking of Moslem terrorists here. They are relative newcomers to murderous intolerance. Communist dictators like Lenin, Stalin, and Mao brutally suppressed freedom of speech at the same time that they murdered millions.
In America the First amendment to the constitution limited the Federal Government from restricting freedom of speech but this has not stopped the modern methods of thought control that we read of every day in our colleges and universities. Just the other day I read that left wing activists have been threatening sponsors of conservative talk radio shows. Broadcasters like Rush Limbaugh have been extremely popular and no liberal equivalent has ever succeeded. Rather than defending to the death the right of conservatives to express their opinions, their opponents are trying to get them off the air.