[blindhippo]

Unions are meant to be effective in situations where the balance of power between capital and labor is heavily tilted towards the former.

In a situation where there is an actual competitive market and people can leverage their skills and experience towards better salaries on their own, the effectiveness of a union is much lower, though there is still industry wide benefits such as normalization of health insurance standards, anti-cartel advocacy, general working condition standards, etc.

I think the police union example is a bit of a bad faith example - there is more to that one than just "union bad, mmmmkay" - it's institutionalized power and would NEVER be a market driven situation.

Teachers, generally speaking, work in a single employer market, meaning the power dynamic is again tilted towards the employer. Without a union, teachers would likely have even worse conditions than they currently "enjoy" in the USA (and frankly Canada). Hell even now they basically work overtime for free due to expected "extra curricular" workloads outside of school hours and in many cases have to supply their own materials just to be able to do their own job.

Yes, there are disadvantages (as there is in all things). But these do not mean that unions are fundamentally broken.