I think its fairly easy to criticise the actions of existing powerful unions, and postulate that the less relevant unions lost relevance exactly due to the same

I think its fairly easy to criticise the actions of existing powerful unions, and postulate that the less relevant unions lost relevance exactly due to the same concerns and lack of monopoly protection. Teachers unions for instance are still very strong on a state-by-state basis, but are disliked because they continuously only promote public schools and do whatever they can do show disdain for private school teachers, and students. This 'us versus them' mentality doesn't endear them to parents who simply want the best education for their children and not necessarily a "public school". Additionally due to teacher's unions, demonstrably bad teachers are difficult to remove from their positions. Police unions act similarly, by closing ranks anytime there's a whiff of a corruption investigation and proposing measures that essentially make police officers a protected class when it comes to criminal investigations against them. It's no surprise that the general public isn't in favour of them. Unions historically can be favoured by the general population, when most people in the general pop are also members of unions themselves. Unions have an us versus them mentality that puts them at odds not only with management, but also with anyone who isn't a part of a union. They make allowances for and have political alliances with other unions, but don't really think about the public good. An example is that if Software Developers were all in a union, we'd probably work it out so that a garbage man's union strike doesn't affect us too badly, so that in the future when we go on strike, the garbage men won't suddenly find that the apps and software they depend on suddenly has zero support. Given this situation, software devs (of the union) would be 'okay' with the other union, but everyone outside of the union would be unhappy because they're left high and dry.