One upside for companies is that the unions are better able to represent the interests of the employees than, for example, the HR department would be able to, simply because of the incentives at play. This could attract more talent to the company, improve retention, and give the company more insight into the employees' needs.

only in theory. in practice unions become just like other orgs where leaders concentrate power for themselves and fail to represent anyone at all. making the situation worse for the employee and the employees.

If that's the inevitable fate of all orgs then why bother creating any kind of society at all?

I can agree that unions concentrate power in imperfect ways, but personally I still think they are an overall improvement on the non-union status quo.

> unions are better able to represent the interests of the employees than, for example, the HR department would be able to

Employees are really good at complaining (at least in the US). Management that is interested in knowing what bothers employees definitely knows without a union.

> This could attract more talent to the company, improve retention

Paying more money works even better. People choose better paying jobs pretty consistently even if it means dropping the union.

> Management that is interested in knowing what bothers employees definitely knows without a union.

Sure, but unions are good at motivating management to care.