In chapter 5 I discuss the two great utopianist social engineering movements of nationalism and totalitarianism. One problem they pose is that they were espoused by intellectuals, including scientists. To turn them aside Popper has to develop his view of social science and of the social organisation of science. From this effort we can extrapolate his view that science is a model for society: science is the knowledge-gaining institution par excellence. Because all institutional initiatives embody conjectures, the society of institutions embodies our aggregate conjectural attempts to realise our aims. Knowledge is a social institution, and social institutions are our attempts to apply our knowledge. 
An analogous gap exists in Popperian epistemology. Its critics wonder why the scientific method works, or what justifies our reliance on the best scientific theories. This leads them to hanker after a principle of induction or something of the sort (though, as crypto-inductivists, they usually realize that such a principle would not explain or justify anything either). For Popperians to reply that there is no such thing as justification, or that it is never rational to rely on theories, is to provide no explanation. Popper even said that ‘no theory of knowledge should attempt to explain why we are successful in our attempts to explain things’ (Objective Knowledge p. 23). But, once we understand that the growth of human knowledge is a physical process, we see that it cannot be illegitimate to try to explain how and why it occurs. Epistemology is a theory of (emergent) physics. It is a factual theory about the circumstances under which a certain physical quantity (knowledge) will or will not grow. The bare assertions of this theory are largely accepted. But we cannot possibly find an explanation of why they are true solely within the theory of knowledge per se. In that narrow sense, Popper was right. The explanation must involve quantum physics, the Turing principle and, as Popper himself stressed, the theory of evolution. 
So the growth of objective scientific knowledge cannot be explained in the Kuhnian picture. It is no good trying to pretend that successive explanations are better only in terms of their own paradigm. There are objective differences. We can fly, whereas for most of human history people could only dream of this. The ancients would not have been blind to the efficacy of our flying machines just because, within their paradigm, they could not conceive of how they work. The reason why we can fly is that we understand ‘what is really out there’ well enough to build flying machines. The reason why the ancients could not is that their understanding was objectively inferior to ours. 
There is the greatest difference between presuming an opinion to be true, because, with every opportunity for contesting it, it has not been refuted, and assuming its truth for the purpose of not permitting its refutation. Complete liberty of contradicting and disproving our opinion, is the very condition which justifies us in assuming its truth for purposes of action; and on no other terms can a being with human faculties have any rational assurance of being right. [ch. II, 26]
Although I am an admirer of tradition, and conscious of its importance, I am, at the same time, an almost orthodox adherent of unorthodoxy. I hold that orthodoxy is the death of knowledge, since the growth of knowledge depends entirely on the existence of disagreement. Admittedly, disagreement may lead to strife, and even to violence. And this, I think, is very bad indeed, for I abhor violence. Yet disagreement may also lead to discussion, to argument, and to mutual criticism. And these, I think, are of paramount importance. I suggest that the greatest step towards a better and more peaceful world was taken when the war of swords was first supported, and later sometimes even replaced, by a war of words.