The only difference between them is that a democracy, at least in principle, exists to serve the people. Corporations expressly exist only to serve themselves. Democracies may face corruption, but there's not even a principle to be corrupted in the case of corporations; in a free market they have no accountability to society.
I suppose you could call co-ops "democratic corporations", in which case governments and corporations are exactly the same, but from that perspective today's corporations would be analogous to oligarchies; they exist to serve their small circle of shareholders. So forgive me if I choose to put my faith in a flawed democratic government instead of oligarchical corporations.
I trust an elected government far more than any for-profit organisation.
I'm just saying, both are ripe for abuse by tyrants, plutocrats and oligarchs. Corporations moreso though, for sure.
If there were no government, you would still have the same problems, only now unrestrained corporations would be at the root of those problems.
Government and Corps are no different in the end. They all seek to perpetuate and consolidate their power over the plebs.