Not necessarily, some are democratic, like some in Sweden. The IWW is an example of an alternative to the centralized unions [1].
But that's the problem. The employee faces the same asymmetry when dealing with the union as dealing with the employer -- a single individual has difficulty driving a change in organizational behavior.
It's harder for an individual to fix a bad union than to leave the company for one without that union, so that's what many people will do. Which makes it even harder for anyone to do it your way, because many of the people who agree that there is a problem will have left.
Is that accurate?
That's especially true when there are other jobs in the same industry and the same city but at a different company.
Emoloyees aren't part of the corporation any more than the widgets they make are.
Which is why they're not democratic, opposed to say cooperatives.
Unions are just corporations for labor sales. If you don’t like your management, replace them with your vote.