Should I answer this question about diversity? There is an optional prompt on my PhD application:


  censoredSchoolName University regards the diversity of its graduate
  student body as an important factor in serving the educational mission
  of the university. We encourage you to share unique, personally
  important, and/or challenging factors in your background, such as work
  and life experiences, special interests, culture, socioeconomic
  status, the quality of your early educational environment, gender,
  sexual orientation, race or ethnicity. Please discuss how such factors
  would contribute to the diversity of the entering class, and hence to
  the experience of your censoredSchoolName classmates.


If I were to answer, what I would write is something about how I grew up in a large family with five siblings all attending college around the same time, so though I come from a middle-class family, I have had to handle much of the financial responsibility of my education. In addition to this, neither of my parents have attained higher than a non-scientific Bachelor's degree, and I have mostly blazed this path under my own independence and ambition.

But I feel that this might not be what the question is really looking for? What I've written above does not make me diverse in the way that I think the University probably wants. I'm a middle-class white male, I will say, which my application has of course already reflected. I'm wondering if I might be better off leaving it blank rather than coming off as forcing a hollow answer, or even pitying myself when there are certainly other applicants with serious disadvantages.
Leave it blank

You don't have to play along with the diversity people, but that doesn't mean there won't be any consequences. 

Throughout my time in undergrad, the US military, and now grad school, I have steadfastly refused to answer questions about my race. And why should I? My father is from Mexico and is still a dual citizen. As far as I can tell, that gives me a pretty good claim to be Hispanic. I am born in Boston, I don't speak Spanish, and I don't particularly like anything Mexican. Am I hispanic? What is my hispanic blood quantum? Am I white? Who cares? 

What ought to matter is the content of your character, or so I've heard. 

Just don't be surprised when people don't want to let you go. I have been called into a senior officer's office (in the military) and forced to answer a question about my race. When I told him it was 'American', he filled out the forms in question for me as white. I haven't always got off easy, but I've done alright in life, and without participating in such racist activities as classifying people based on their skin color. 

PS: The original form of your question was just fine. If you have sneering contempt for this kind of diversity question, then you do. Don't let people bully you into thinking your opinion isn't valid.