In his book, The True and Only Heaven: Progress and its Critics, Christopher Lasch writes:
Niebuhr endorsed G.K.Chesterton’s observation that tolerance is the attitude of those who do not believe in anything.
Could you reconstruct the original quote?
Lasch was using the word “tolerance” for what Chesterton generally termed “impartiality.” Chesterton deplored impartiality, which he equated with indifference, but he generally applauded tolerence, which he contrasted with bigotry — unless the tolerance in question was really a mere mask for indifference. Chesterton expressed these thoughts in a very large number of places and in a many ways. The closest to Lasch’s quotation is probably:
Impartiality means at best indifference to everything . . . [Illustrated London News, July 5, 1919]
Or (from the web page of The American Chesterton Society):
Impartiality is a pompous name for indifference, which is an elegant name for ignorance. ["Puritan and Anglican," The Speaker, December 15, 1900. Reprinted in The Chesterton Review, vol.9, no. 4]
More from the Illustrated London News:
Modern toleration is really a tyranny. It is a tyranny because it is a silence. [October 10, 1908]
Our real error in such a case is that we do not know or care about the creed itself, from which a people’s customs, good or bad, will necessarily flow. We talk much about ‘respecting’ this or that person’s religion; but the way to respect a religion is to treat it as a religion: to ask what are its tenets and what are their consequences. But modern tolerance is deafer than intolerance. The old religious authorities, at least, defined a heresy before they condemned it, and read a book before they burned it. But we are always saying to a Mormon or a Moslem – ‘Never mind about your religion, come to my arms.’ To which he naturally replies — ‘But I do mind about my religion, and I advise you to mind your eye.’ ["Mormonism," The Uses of Diversity; Illustrated London News, May 13, 1911]
The new bigot says, ‘I will not argue with you, because I know you agree with me.’ (April 28, 1906)
In real life, people who are most bigoted are the people who have no convictions at all.
Bigotry may be roughly defined as the anger of men who have no opinions.
Chesterton goes on to expand that idea as follows:
It is the resistance offered to definite ideas by that vague bulk of people whose ideas are indefinite to excess. Bigotry may be called the appalling frenzy of the indifferent. This frenzy of the indifferent is in truth a terrible thing; it has made all monstrous and widely pervading persecutions. In this degree it was not the people who cared who ever persecuted; the people who cared were not sufficiently numerous. It was the people who did not care who filled the world with fire and oppression. It was the hands of the indifferent that lit the faggots; it was the hands of the indifferent that turned the rack. There have come some persecutions out of the pain of a passionate certainty; but these produced, not bigotry, but fanaticism — a very different and a somewhat admirable thing. Bigotry in the main has always been the pervading omnipotence of those who do not care crushing out those who care in darkness and blood. [Heretics, chapter XX, "Concluding Remarks on the Importance of Orthodoxy"]
And what applies to the family applies to the nation. A nation with a root religion will be tolerant. A nation with no religion will be bigoted. ["The Sectarian Society," A Miscellany of Men]
There is something that is higher than impartiality . . . the living impartiality of the imagination rather than the dead impartiality of the reason. (“The Case for Macaulay,” A Handful of Authors)