What you are referring to as tax money going to the unions is a false way of looking at it.

The moment the money generated from taxes gets paid out to a public employee, it is no longer TAX money, but that employees money. And once the union receives that money, it is no longer that employees money, but the union's money.

If you are going to insist that money is still tax money then you have to admit that money spent by WalMart that they receive from public employees shopping in their stores is still tax money, and thus much of the money that WalMart (or any other large corporation that sells goods) spends on SuperPACs and other political donations is tax money.

Hell, at this point, going by your assumption that the money paid to unions for dues is tax money, most money is this country is probably tax money.

Unions would not be necessary if it wasn't for the natural inclination of the fat cats to underpay and in other ways abuse their employees. If employers had paid their employees well, and treated them well, the unions would probably never been formed. Without unions, American workers would be as badly abused by employers as Chinese workers are.

(NOTE: I randomly chose WalMart, but this goes for any corporation that sells goods and services).