I'm NOT defending him. I just think Romney would score points with voters if he did.
Personally, I didn't WANT Obama to give in to the Birthers. I found the whole thing ridiculous, and thought that Obama had nothing to prove. The accusations were an insult to the office of President.So you are going down the path of "I don't truly believe Trump, but it would be nice if Obama released his birth certificate"
The difference is... Obama has released ten years of his tax returns, and so have all Presidential candidates, except, as you said, Reagan and Kerry. Even prominent members of the GOP want Romney to do it.
So this request is not NEARLY as unreasonable as wanting Mr. Obama to show his birth certificate, seeing as that is something that NO President has EVER been asked to do.