I think it's less the idea of the 'noble savage' thing but more a matter of perserving something beautiful. I find other languages fascinating in the way of how those people think. I find when I switch between English (my main) and Arabic (due to dad's side of the family) I think slightly different, more than just sentence structure and grammar, something like tracing why we use the words we do show what used to be a cultural priority. If you read that website's thing about each of the endangered languages you learn what those people valued most. I think that's something worth protecting purely because everyone thinking the same way is just damn boring.