As has been pointed out many times, apparently fruitlessly, the unions have lobbied hard to ensure that you don't always have a choice in the matter.

Even in the US, you are not forced to join a union.

You might have a union negotiate minimum pay and conditions on your behalf, but that doesn’t stop you from negotiation beyond that individually.

That is simply not the case. Google "Right to work" and "Union shop." At a minimum you're required to pay dues to the union.

Forcing workers to either join or pay tribute to a middleman isn't OK.

It seems entirely reasonable to pay dues for a benefit you receive. I don’t see why that’s such a big deal. You still don’t need to be involved in organising.

It’s entirely ok for the majority of workers to democratically decide that they shouldn’t have to fight for benefits that others get for free. Unions aren’t middlemen, they’re just the majority of workers in a workplace organising themselves.