Should I answer this question about diversity?
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.