Some bad unions: all unions are awful and the solution is to not have unions.
Unions are not benevolent. They are bureaucratic organizations that want to grow in power and resources just like a corporation. Their interests just happen to be orthogonal to corporate interests which can be beneficial for employees.
I suppose you could describe many groups of people as corporations by another name so I'm not sure how far that gets us, and I tend to treat groups of people large enough to have emergent behaviours as essentially amoral anyway.
Your market share comments are interesting. I remember Matt Levine making an observation about Uber's 'contractors', if they attempted to unionise could be guilty of price fixing, because they're supposed to be competitors. The corporation seems to be another step along where price fixing within the corporation is allowed, and the union goes a step further again by making monopolistic behaviour ok.
As a society that has decided that a corporation can decide how to organise itself and work together internally, but also a society that has decided that monopoly, or at least the abuse of that monopoly is wrong, these seem to be interesting exceptions.
Portland is also undergoing an tremendous unionization battle at a local burger chain (Burgerville); one or two of the shops have successfully unionized, while the rest are still fighting for their right to organize. That's because unions here are at the shop level, and there just couldn't be one burger union that dominated all burger-making.
Because unions gets more powerful than any company and can leverage said power against both workers and employers.
Lets take SAG-AFTRA as an example, a union many here at HN says the software industry should mimic. Their contracts with their workers states that the workers are not allowed to work at non-union shops, and their contracts with shops states that they are not allowed to work with non-union workers. This means that you as a worker has to join the union if your workplace unionize no matter if you feel it benefits you or not, and as long as the union control most workers any larger workplace will be forced to join or they will lack workers.
Why would workers not just stop being in the union, since it costs $3k to join and 2% of your salary to stay? Because the entire workforce at a union shop has to quit at once, at the same time the shop has to decide that they are not a union shop any longer. Do you think that will happen? No, of course not, weeding out a union in such a situation is way harder than starting the union in the first place. And even if they organize, the union could organize a picket in return to harass the shop and its worker into compliance.
Edit: Also PR and propaganda could easily make workers believe the union is good for them even if it isn't, kinda like how poor whites think that Republicans are on their side.
Or a majority has to elect new leadership in the union who will replace the problematic rules.
Or a majority (either of the whole membership or of workers in a defined subarea) need to vote to decertify (and optionally replace) the union.
Because of these, “everyone has to quit at once” is literally never an issue.
> Also PR and propaganda could easily make workers believe the union is good for them even if it isn't
Sure, but workers opposed to the existing union and employers and union parent organizations competing with the parent of the existing union (or wanting to become the parent of there is no current parent) are all able to deploy “PR and propaganda” (two different names for the same thing) against the established union, too.
"The Market" (or however you want to think about it) is not perfectly efficient - if it were, there would never have been any motivation to form unions because every employee's requirements would already be perfectly reflected in the companies they chose to work for. Rather, sluggish network effects and other non-invisible-hand structures dominate immediate results.
All power tends to concentrate. When it gets large enough, it attracts those who seek and hold power for their own ends rather than any benevolently stated goals. Your scenarios are straightforwardly mitigated by union leadership directly appeasing the leaders of such movements, the same way monopolist companies buy out possible competitors to keep a stranglehold - the creation rate of competition is itself limited.
I don't know too many specifics about SAG-AFTRA itself, but its hold over the entire industry is a good indicator that it is indeed too large. Its size implies politicking on the order of at least a city government. Conversely, that size may also be the minimum necessary to engage in collective bargaining across different production companies, and so any general top-down reform is a bit hazy. My only direct experience with this is seeing casual SAG actors having to do a bunch of extra paperwork to participate in a strictly non-profit hobby short film production. It seemed quite ridiculous and onerous, until I thought about the neighboring gradient of low-budget for-profit film production.
Also entertainment unions provide way more services eg training, chasing late payers for freelancers and running the "call first list" - this is the list of problem employers.
The structure of labor law makes it just as possible for workers with a particular employer or in a particular job class with an employer to decertify—and, if they wish, simultaneously replace—a union (or for a union local to dissociate from a parent organization) as it is to organize one in the first place, which doesn't prevent parent union organizations from getting large, but does limit the success of ones that, in doing so, fail to meet the needs of their members in particular workplaces.