Functionalists proper, those of the 1920s and 1930s, did not refer to God but rather to demands of the "Zeitgeist", "Modern Epoch" or "Machine Age". Whether references were to God, Nature or History (references to the Zeitgeist, Epoch or Age are of course references to the authority of History) they referred to Purposes of an other-than-human Intelligence. Such Purposes, in not being human purposes, were allegedly no longer subjective but objective, and as such they sanctioned the vision of objective design.
In suggesting that the aesthetic demands of the market were illegitimate or by definition questionable, functionalist architects and designers proclaimed in effect their artistic autonomy and joined (mentally, that is) the coveted ranks of fine artists, as Brent Brolin convincingly argued in his book Flight of Fancy . Modernist architects and designers were re-enacting the liberation process through which painters and sculptors arrived at the status of "fine" artists.
As the modernist designer's claims to authority increased, the user's status became more and more precarious. Direct references to users, or clients, when they appear in the functionalist texts, are almost invariably of an edifying bent, suggesting that the modernist architect is in possession of authority to decide what is best for them, both in the functional and in the aesthetic sense.
Since functionalist design philosophy claimed that the essence of designing was the search for intrinsic solutions, the adherent of the functionalist design philosophy was precluded from understanding that the 'intrinsic solutions' he arrived at were based on his own choices and that he - not functions, materials, constructions, or the modern epoch - was responsible for those solutions.
The more [the designer] trusted that the functional starting point guaranteed an objective aesthetics, the less he understood that his formal solutions were in fact addressed to the aesthetic sensitivities and artistic preferences of his own peers, plus a minority of others, endowed with "cultural capital", who shared these sensitivities and preferences.