Surveillance. It is used by every tyranny to lock in place an uneven arrangement of power. When the mighty know all about you but common folk know little in reverse, then without accountability you can only have despotism, as shown by 6,000 years of recorded history.
But new technologies do not have to lock in perpetual Big Brother. The spread of tools like cheap cameras and instant sharing might lead to the antidote against Big Brother. That is, if we learn the lessons taught by both history and science. The answer is not to hide from elites but to hold them accountable with light.