The path of despite and in spite of from their French origins to their modern usage leads through a process of semantic bleaching, where the lexical meaning fades in favor of function, to reach a state of grammaticalization, where despite can only be defined by what it does — a concessive preposition or conjunction — rather than what it means.
In this particular case, it is a matter of the affect or attitude inherent in the word — contempt, defiance, strong objection — reducing to a mere contrast.
and that riall chyrche of Sancta Sophia robbed and despoilled and the reliques and ymages and the rode [rood, i. e., cross] drawe aboute the stretes whiche was done in despite of cristen feith … William Caxton, Chronicles of England, 1480.EEBO
A modern reading of in (de)spite of here is impossible, as those who paraded about the icons and reliquaries of Hagia Sophia were not themselves Christian. The meaning here is still lexical: in contempt of.
Other early texts are more ambiguous:
… they helde in perpetual pryson, the most noble emperour Valerian in despite of all the romaynes and many other princes, whiche wrote for his delyueraunce … Roger Ascham, Toxophilus the School of Shootinge, 1545. EEBO
But if in all this, i had said nothing, but that stil in spite of all that hath beene said, these and the like masterpieces of the world, would of force bestow some happinesse on man, … Francis Rous, The Arte of Hapines, 1619. EEBO
Others in a great river haue beene carried away by the strength of the streame in spite of their skill in swimming, … — Stephen Bradwell, Helps for Suddain Accidents, 1633. EEBO
… when I haue harried him thus two, or three yeare, though he sue in forma pauperis, in spite of all his thrift, and care he'le grow behind-hand. — Philip Massinger, A New Way to Pay Old Debts (comedy), 1633. EEBO
Discerning the level of defiance in these passages is, of course, subjective, but while one might keep someone prisoner in defiance of those demanding his release, it’s difficult to see a swift current “defying” someone’s swimming skills or a man his own thriftiness. These sentences, however, are cherry-picked from tens of others where some degree of affect, and thus lexical meaning, is still possible, even probable.
Around the 1680s and 90s, passages more patient of a modern, grammatialized usage become more frequent:
… for air is so subtle a matter, that it will be apt to insinuate it self by degrees into the tube, in spite of all the quick-silver within it, … — John Smith, A Complete Discourse [on the Barometer], 1688. EEBO
… but in spite of all that art can do, men will abound in their own sense, and there will for ever be as many diversities of opinions, as there are of palats. — Benedict de Spinoza, (unknown trans.), A Treatise Partly Theological, and Partly Political, 1689. EEBO
Demosthenes did by great resolution and almost infinite pains, and after a long habit, alter the natural imperfection of his speech, and even in despite of nature became the most eloquent man perhaps that ever lived. — John Tillotson, Six Sermons, 1694. EEBO.
And in the 18th c., grammaticalization seems complete:
Under your auspices, this lord, in spight of all his unpopular actions, carries away the hearts of the people, not by the fineness of his address, or any particular deset, but by your favour.
— Thomas Brown, “A Declamation in Praise of Wealth_, Works, 1744.
