Here's an important question: Who owns the fruits of your labor? If a percentage of what you earn is forcibly taken from you-- and by 'forcibly', I mean 'against your will' and with the coercive use of force (after all, if you don't pay your taxes men will come to arrest you, men with guns who will kill you if you resist)-- then you are a slave.
I'll put it another way: Would **** become morally acceptable if Congress passed a law legalizing it?
If you take the position that "No, idiot, **** is not nor would ever be morally acceptable", isn't it just as immoral when Congress legalizes the taking of one person's earnings to give to another? Surely if a private person took money from one person and gave it to another, we'd deem it theft and, as such, immoral. Does the same act become moral when Congress takes people's money to give to farmers, airline companies, Sadaam Hussein, or an impoverished family? No, it's still theft.