Well, there's two different questions here... the first is what is in fact true about human communication, and the second is what's right and wrong.

I might believe, as Xachariah does, that language is fundamentally a mechanism for manipulating the behavior of others rather than for making true statements about the world... and still endorse using language to make true statements about the world, and reject using language to manipulate the behavior of others.

Indeed, if I were in that state, I might even find it useful to assert that language is fundamentally a mechanism for making true statements about the world, if I believed that doing so would cause others to use it that way, even though such an assertion would (by my hypothetical view) be a violation of moral principles I endorse (since it would be using language to manipulate the behavior of others).