Heck, look at the lineup before the final nomination this year - every candidate (and the final nomination) had serious issues and people voted for them anyway, so squeaky clean is not the problem - full disclosure is.
If more people came to see that perfectly capable people are often not squeaky clean in largely irrelevant matters we would all be better off.
Imagine a country where politicians don't live in fear that the public might learn they sometimes spark a bong, or once cheated on their spouse, or like people of the same gender as themselves from time to time.
Of course, it's just his taxes, and I feel like the only reasoning people are upset with Romney over this is that they are thinking "What's he hiding? If you have nothing to hide..." which most of us probably dismiss as bad thinking in the usual context. If the People want to make it a law for candidates to disclose their tax information, let it be done, right now he's just breaking a 40 year old precedent. (It seems McCain did the same thing and only released two years--was there an outcry about that? I don't remember, there were so many other juicier attacks. If "you're rich!" is the only thing they can attack you on you're doing alright.)