The best argument for preserving endangered languages, ironically, is the strong form of the Sapir-Whorf hypothesis--which linguists flatly reject. Given how hostile most of them are (if Pullum and his gang on Language Log are anything to go by) to even the soft Whorfianism of Boroditsky et al., it's quite galling that these same linguists, who assert the absolute fungibility of human languages, also stress the vital importance of preserving each and every one of them.
And given that linguists use as an insult the term "prescriptivist"[1] for anyone who wishes to preserve or establish particular linguistic usages--even if for wholly benevolent reasons, such as the removal of inconsistencies for the benefit of non-native speakers--how can they then go and support efforts to actually increase the number of speakers of some dying tongue? Isn't that awfully prescriptivist of them, dictating not just how others should use a particular language, but even which languages they should be speaking?
And given that linguists use as an insult the term "prescriptivist"[1] for anyone who wishes to preserve or establish particular linguistic usages--even if for wholly benevolent reasons, such as the removal of inconsistencies for the benefit of non-native speakers--how can they then go and support efforts to actually increase the number of speakers of some dying tongue? Isn't that awfully prescriptivist of them, dictating not just how others should use a particular language, but even which languages they should be speaking?
[1] http://languagelog.ldc.upenn.edu/nll/?cat=5