Tax is only theft if you can argue that there is some law that supersedes the government's law that they can raise taxes.
You need to learn to differentiate between the legal, the moral and the ethical realms. Taxes are not legally theft but if we assume that correctness is defined by law, then where is the reasoning behind changing laws?
Also, if government has the authority to rob and call it tax, then any of us can just band together with some guns, call ourselves government and do the same, and that is fine?
The big moral question then is: are various serious crimes, in this instance robbery (with violence), somehow okay because we legalize them in the name of government? The same applies even more so to extrajudicial homicide.
Okay, apparently I wasn't clear. I was trying to argue that simply taking something by force does not make it robbery or theft. I gave the examples of the bailiff and the police confiscating stolen goods. What, then is the difference between the police confiscating stolen goods and a bank robber taking cash from a bank since both involve taking goods by force?
My answer was that the thief doesn't have a legal claim on the property that the police confiscates, whereas the bank does have a legal claim on the money stolen from it.
So whether the government is robbing you depends on whether they have a legal claim on the money they are taking. Simply taking it by force is not enough.
I don't expect you to agree with me now, but is it any clearer where I am coming from?