A purity of interest is evanescent...Purism cannot accept the evanescence of purity; it imposes stereotyped surrogates for pure interest. Purism aims to to put purity at the disposal of the will, whereas purity of interest is something which needs to be cared for and carefully treated... So the desire for purity of interest turns into purism if sustained in conservatism. (Max Deutscher, Subjecting and Objecting).