> That we vote to pay for through our elected representatives; the same people who directly determine budgets, salaries and have political skin in the game to get re-elected at the time of contract negotiation and have firing power.
All of that applies to employing people just as much as to other ways of spending public money. (Yes it's hard to fire a public employee - but it's also hard to cancel a public works project).
> Public projects are not the same as public salaries. A highway is not drawing a salary from the treasury, but the people who work on it are.
Public money is spent, private individuals and/or businesses benefit. Whether it's structured as an employment contract or a public works project seems pretty irrelevant.
> People decide all the time whether unions are actually beneficial for them in the private sector and many times vote against it either by choosing non-union employers where both are an option or by voting for or against joining a union when a unionization vote occurs.
Which is their right (I think it's foolish except maybe for upper-class people in fields where individual performance is directly measurable, but it's their choice), but how is that any different for a public employer vs private employer?
> A Google employee working on a government project did not elect the Executives who approved the project and his salary, even if he may have elected the Senator that said it was a good idea for Google to handle it.
What difference does that make though? That executive is hardly going to turn down a profitable contract even if they think it's for something stupid, so you're not bringing in any more accountability on any aspect that's actually relevant. (And in practice a public employee is going to be in a very similar position: there will be several layers of unelected civil service administrators between the person they vote for and the decision about how much they get paid).
> Private advocacy groups have to compete with other moneyed interests. Public-sector unions do not.
There are plenty of moneyed interests opposing public-sector unions.
> There is no one else that is going to pay government salaries except the government, and they get their money by taking it from people who earned it.
Your bias is showing. Many government employees earn their money (including many teachers) and many taxpayers don't.
> Unionized employees of all stripes tend to vote as a bloc because taking collective action is their raison d’être.
Sure, but that's exactly the same for advocacy groups, neighbourhood associations and so on.
> The government is not approving contracts between private sector companies and private sector unions. They are approving contracts between themselves and public sector unions, and have hiring and firing power over the negotiators at the table representing the public’s interest.
Right, but they negotiate contracts or quasi-contracts with all sorts of collective organisations - businesses, business groups, professional associations, residents' associations, advocacy groups - all the time, under the same kind of conditions.