There is a difference between voluntarily giving somebody an amount of money and having the same amount of money taken away from one, maybe even without one noticing it at first. Even though the economic situation might be the same, it is the loss of control, of sovereignty over one's own affairs, which we find troublesome. Likewise, hardly anyone, when buying something from a complete stranger, would assent to the idea that one is to hand over one's wallet, let the seller take whatever he or she sees fit, and return the wallet, with the buyer only being able to find out much later, how much was taken.