John Stuart Mill according to Feyerabend in Philosophical Papers, (Problems of Empiricism, Chapter 4, Two models of epistemic change: Mill and Hegel).
p. 65 “What has made the European family of nations as improving, instead of a stationary, portion of a mankind? Not any superior excellence in them, which, when it exists, exists as the effect, not as the cause, but their remarkable diversity of character and culture. Individuals, classes, nations have been extremely unlike one another: they have struck out a great variety of paths, each leading to something valuable; and although at every period those who traveled in different paths have been intolerant of one another, and each would have thought it an excellent thing if all the rest would have been compelled to travel his road, their attempts to thwart each other’s development have rarely any permanent success, and each has in time endured to receive the good which the others have offered. Europe is, in my judgment, wholly indebted in this plurality of paths for its progressive and many-sided development“.
Also Feyerabend’s quote from the preface
“The reader will notice that some articles defend ideas which are attacked in others. This reflects my belief (which seems to have been held by Protagoras) that good arguments can be found for the opposite side of any issue.”