This is like saying a political party leads to what it members want it to lead to, since it's a democratic entity. In practice different members want different things, and it easily ends up as political games with mismatched incentives.
So the argument against forming a new political party is that there are political parties that do things you disagree with?
I think the argument is that a union is more like a party in a winner-take-all system than a party in a multiparty system.
The alternative is the employer winning in a two party system.
Maybe. Or maybe that's a false choice. Honestly I'm generally unconvinced by "it's us or them" arguments.
That's not necessarily a given. To be fair we also technically live in a democracy with a democratic process. Many would argue that the views of the majority are not reflected.
Are you saying that the views of the majority are better represented in dictatorships?
Negative.
It doesn't work that way. Boeing employees don't get to dictate what Boeing as a business does, only how it interacts with and compensates its workers. No union is going to change that.
Well they do with Airbus, and Volkswagen, and Bosch, and DHL, etc., because in Europe it is not uncommon for unions to have board seats. In Germany this is mandatory for corporations of a particular size, regulated by the works constitution act.