Argument- Any knowledge when sought with an ulterior motive - biases the study towards that motive instead of the knowledge itself, unadulterated. As a result, aspects of the knowledge that do not cater to or do not seem highly relevant to the objective are ignored or ill-understood.
Counter- Neccessity is the mother of invention, etc. All engineering came about as man learnt to apply science in order to solve other problems. A step further - the desire to know is always given birth from a different need - say a desire for food, or shelter, or entertainment or pride. So the "other bad impure objective" is the very reason that the "desire to know" was born.
Will need examples.