I must admit I am lost.
If the argument goes that every language is unique and that by keeping every language inside WMF (let us forget about extinct and artificial languages for the moment, they are not an issue here) actually helps establishing the neutral point of view, then the preservation of endangered languages IS a goal of WMF. Obviously, not a primary goal, but a secondary goal.
To me, if we say this is NOT a goal of WMF means WMF should not care whether the language is endangered or not. It only should care about the most efficient way to spread of the information. Just, you know, counting bytes per unit time. Then, indeed, a question can be raised why the languages with the purely bilingual support should be supported.
I can not really connect the two things. To me, they sound like mutually exclusive.
Btw, I do not see how asking questions can make feel somebody second sort. Answering questions and taking decisions can.
Cheers, Yaroslav