For example, suppose I want someone to think that making use of human biases is a bad thing, and so I label that activity using words with negatively weighted denotations like "exploit" and "dark."

What have I made worse, by so doing?

You seem to be confusing rationality with suppression of emotion. As Eliezer points out here, there is nothing wrong with feeling emotions that accurately correspond to the territory. There is similarly nothing wrong with promoting such emotions in others. The "dark arts" really are things humans should avoid using, as such there is nothing wrong with associating them with negative emotions.