The notion of approaching a certain text without presuppositions is, I think, a pretty hard one to defend. Personally, I'm a fan of traditional-style close reading, I just think what matters is the audience you're intending to share the reading with. There has developed, I'm sure, a sort of hierarchy that is organized something like this: Theorists--> Critics --> Creative Writers --> Reading Public (assuming we still have one). Most productive thinking comes out of the continuity between theorists and critics, and a similar continuity between Critics and writers. But, theorists and individual writers rarely have anything to say to each other, except to dismiss the various claims of the other, outright.
I tend to think that close reading is the common denominator between the three academic groups, and is the one that should be focused on to intentionally bridge those otherwise chasm-like gaps. It's definitely frustrated me reading some theorists, seeing them cite a particular passage, and use like three words from the passage and then motor on... Why invoke the piece if you don't use it to it's fullest potential? Take the logic of the individual sentences to their end, etc... But I'm equally miffed when I see an author talk about the total irrelevance of theory. So much theory has explanatory power beyond an individual text that it can't simply be coincidence....
Anyhow, to the original question: I point them in the direction of the two articles I've seen in the Chronicle of Higher Education: one notes that humanities students are better critical thinkers and retain more information, and the other discusses the enhancement of an individuals empathy through exposure to creative writing and its various characters and manifestations. There are solid social reasons for the studies of the humanities.
That's about it. I'm a little philistine.