You asked how would I respond to the question that Mitt was asked? That's how.
The question asked of Romney is the same sort of question. It assumes what it is trying to prove. It assumes that Romney is trying to do X, just like my question assumes that you've beaten your wife in the past.
That's what I was implying in my first post. The question was asked with the purpose of being unanswerable by Romney. Romney's response is natural, since he doesn't have any response that could satisfy their question. But at the same time, the question posed is legitimate if aggressive, since opponents of Gay Marriage don't really care about how gay couples would justify not being married to their kids.