Note the essential similarity between the logic of Sartre (as discussed in a previous post) and the logic of Chesterton in the following two passages.
when we say that man is responsible for himself, we do not mean that he is responsible only for his own individuality, but that he is responsible for all men. [... I]n choosing for himself he chooses for all men. For in effect, of all the actions a man may take in order to create himself as he wills to be, there is not one which is not creative, at the same time, of an image of man such as he believes he ought to be.
(source: Existentialism is a Humanism, Jean-Paul Sarte 1946)
Man can be defined as an animal that makes dogmas. As he piles doctrine on doctrine and conclusion on conclusion in the formation of some tremendous scheme of philosophy and religion, he is, in the only legitimate sense of which the expression is capable, becoming more and more human. When he drops one doctrine after another in a refined scepticism, when he declines to tie himself to a system, when he says that he has outgrown definitions, when he says that he disbelieves in finality, when, in his own imagination, he sits as God, holding no form of creed but contemplating all, then he is by that very process sinking slowly backwards into the vagueness of the vagrant animals and the unconsciousness of the grass. Trees have no dogmas. Turnips are singularly broad-minded.
If then, I repeat, there is to be mental advance, it must be mental advance in the construction of a definite philosophy of life. And that philosophy of life must be right and the other philosophies wrong. Now of all, or nearly all, the able modern writers whom I have briefly studied in this book, this is especially and pleasingly true, that they do each of them have a constructive and affirmative view, and that they do take it seriously and ask us to take it seriously. There is nothing merely sceptically progressive about Mr. Rudyard Kipling. There is nothing in the least broad minded about Mr. Bernard Shaw. The paganism of Mr. Lowes Dickinson is more grave than any Christianity. Even the opportunism of Mr. H.G. Wells is more dogmatic than the idealism of anybody else. Somebody complained, I think, to Matthew Arnold that he was getting as dogmatic as Carlyle. He replied, “That may be true; but you overlook an obvious difference. I am dogmatic and right, and Carlyle is dogmatic and wrong.” The strong humour of the remark ought not to disguise from us its everlasting seriousness and common sense; no man ought to write at all, or even to speak at all, unless he thinks that he is in truth and the other man in error. In similar style, I hold that I am dogmatic and right, while Mr. Shaw is dogmatic and wrong. But my main point, at present, is to notice that the chief among these writers I have discussed do most sanely and courageously offer themselves as dogmatists, as founders of a system. It may be true that the thing in Mr. Shaw most interesting to me, is the fact that Mr. Shaw is wrong. But it is equally true that the thing in Mr. Shaw most interesting to himself, is the fact that Mr. Shaw is right. Mr. Shaw may have none with him but himself; but it is not for himself he cares. It is for the vast and universal church, of which he is the only member.
(source: Heretics – Christian Classics Ethereal Library)
I suggest that it is worth meditating on how such a similarity comes to be.