Unions are cartels of sellers of labor.
If they're good or bad is another matter.
If they're good or bad is another matter.
But a cartel is never required, since businesses competing with each other is the goal of a free market.
I would agree that if unions become more powerful than businesses, so it ends up single-business vs "union-of-unions" you can get the same effects.
Hopefully the asymmetry is clear though. Cartels are never permissible in a free market, but unions often are because of the need for labour to compete "on the same terms" as business.
ie., the mere existence of a union isnt a sign the market is non-free; whereas the mere existence of a cartel is.
It’s pretty clear what you think though.