Might it not be more accurate, chronologically, to trace the origins of 
'scientism' in American economics to the (old) Institutionalists, in 
particular to Veblen?  One thing is certain, Wesley Mitchell and the NBER 
antedated Tingergen's pioneering attempts to build quantitative 
macro-models.

It may also be plausible to associate scientism with 'market socialism', as 
exemplified in the work of Lange, Lerner and Taylor. See for example F. M. 
Turner's presidential address to the AEA of 1929. At least since the 
beginning of the 20th C there was a growing feeling, among Anglophone social 
scientists on the political left, that human social phenomena could be 
analysed as determinate rational processes, and that the ills of human 
societies (as diagnosed by the political left) could be prescribed for in a 
truly scientific manner. Not until Mises and Hayek, I think, was this 
taken-for-granted assumption seriously questioned among British and American 
economists. It was certainly alive and well in the Cambridge of the 1950s, 
where the very few dissenters (Bauer, Denison) were ignored and 
marginalised. In backward, intellectually isolated Australia it survived as 
late as 1964, where Trevor Swan once said to me, 'of course I'm a 
socialist'.

But if we are really interested in the history of economic thought, we might 
well discover economics scientism in Quesnai and the other 'Physiocrats'.

Anthony Waterman