"Power corrupts, absolute power corrups absolutely." (Lord Acton 1834-1902).
"Unlimited power is apt to corrupt the minds of those who possess it" (Pitt the elder 1776-1788).
We cannot all be equal in all things. Honest men and women tend to hang back from power because they do not yearn for it, but there are those in all nations and all levels of society who will with good intent seek power, but become corrupted by it. It is human nature. There are some systems that have control mechanisms, but it often takes too long for them to function. In some countries, there is no such mechanism that works the levers of the law to return matters to equilibrium. An example of the former is the UK, the latter, Spain, but even in the UK the maintenance of law regularly spins out of control because someone in charge looses their moral sense to the opiate of power (usually accompanied by money).
The great leveller is revolution, but in every regime chage I have ever seen or heard of there are those waiting for a vacuum enabling them to step up and grasp the reins of powerin the name of the people. You end up with a despot. It's the way of the world, there is no stopping corruption because it permeates at all levels through society, only by the ballot box can you attempt to control it. Spain is still so close to dictatorship that neither the people, nor the politicians have grown used to the rule of law. Give them a century or so and a reasonable accountable system might evolve.