Power tends to reinforce and bolster itself.
This is a rule that is universal. Whether it is public or private, it does not matter. The first person to reach the mythical hill will build his castle. And when he has that castle he will build a guard, and with that guard he will expand its walls.
Governmental, democratically elected power is a measured evil theoretically checked by the people who elect it. But, no matter how good the intentions of a particular program are, it will grow . Parking tickets once meant to encourage people to do their business quickly and ensure that there is always a place to park your car in a city become an expected line item necessary to fund schooling systems. Schooling systems whose founders originally hoped to spread literacy to the common people become a means of teaching and asserting the legitimacy of the current order. Intelligence agencies, perhaps at some point agreed upon as a defense measure against other state actors, eventually by the same tools become a way of controlling the populace via surveillance, violence, and disinformation. The power, once vested, inevitably is taken for granted, then outright abused.
Private power is much more unchained and insidious. Unchecked private power inevitably devolves into an unchecked governmental power. It can do so at its own hand - as landed nobles did in the classical and middle ages - or, it can co-opt and usurp existing institutions of any size to meet its own needs as happens frequently in the modern West. Economic power inevitably transforms and manifests itself into a physical, or legal power which is then used to ensure that those that hold that economic power continue to hold that economic power. It is such that the richest families in Florence 500 years ago, are the same families that dominate the wealth of Florence today.
Russia is the ultimate example of these sorts of problems. After rapid privatization, chaos, and devastation emerges a small class of former officials turned oligarchs who have in essence perfectly blended private and government power into one well greased, malicious machine that implements and asserts the interests of a small group of people whose only real merits were being first on the scene when the walls began to crumble. Total power has been crystallized, while the people who occupy the normal to lower rungs have very little hope of rising anywhere near that top, or challenging the existing power structure without fear of outright murder. The United States has managed to implement a similar incestuous private-public power system with higher levels of convolution and obfuscation. You can look at books like Manufacturing Consent to show how that system is built out.
The better technology gets, the worse these power dynamics can crystallize themselves. Once upon a time all it took to cripple a king was a bunch of angry peasants with scythes and pitchforks. Or a factory owner, a mine, or whatnot with barricades and guns. Or a 20th century government with guerillas and cells. But with strongly armored weapons, missiles, jet engines, white phosphorus, remote and automated drones: what check could people provide to unjust power? Even if you didn't limit gun ownership, fighting against an entity with tools like that and no fear of using them would be laughable proposition.
What will happen when those with economic power don't just use it to stamp out competition/dissent, or hoard critical resources, or spread propaganda, but actually to change their very DNA? Class divides will no longer be a matter of lack of education, or opportunity, or circumstance, but of practically species as haves will begin to seriously differentiate themselves from the have-nots. It's very likely that you will not see yourself on the favorable side of this divide.
Immortal organizations can always have a change of hands and thus a chance for a change of heart or a grave misstep, but when not even death can be a hard limit on the accumulation and centralization of power, what then? There, will be the point of no return; it would be the ultimate crystallization of power, where there will be no hope for anyone left behind to catch up again as a small cabal of individuals begin accumulating power faster than the pie will ever hope to expand.
The only way to prevent the crystallization of power, is to make such power accumulation impossible. To enslave one, to exert unjust power on one man, is to exert such power against all. Let no man hold economic power or otherwise over another, willingly, or unwillingly. If we do not hold to this maxim, if we do not build structures which safeguard liberty and damage the ability of any one group or set of individuals to assert a meaningful level of power, if we ourselves do not collectively actively assert against power-accumulators, power will slowly centralize and thereafter attempt to crystallize itself into greater and greater structures until they become nigh impossible to break.