Why we always will need checks and balances

Always.

The New York Times:

For at least a year before the 2004 Republican National Convention, teams of undercover New York City police officers traveled to cities across the country, Canada and Europe to conduct covert observations of people who planned to protest at the convention, according to police records and interviews.

Chet at Vanity Press notes:

You know, there's something that most civilized democracies figured out a while ago: if you give the government and its various branches unlimited power with no oversight, then the government will abuse that power. Not might abuse it -- will abuse it.