While I agree with the idea that a government should make as much information as possible to the people it serves, it's just plain naive to think that governments shouldn't have any secrets.
For example:
- Personnel records
- Bank details for accounts containing huge sums of money belonging to the government
- "Where do we keep enormous quantities of " insert dangerous item/substance here
- "What are the security arrangements for " insert dangerous/valuable item/substance
And a heck of a lot of other things that the people wouldn't like to see end up in the wrong hands.