Arguing the Morality of Taxes

Depending on the circles you hang out in this may be a common scene for you. Last night I witnessed a not uncommon sight in libertarian circles. A group of libertarians were arguing (surprising, I know) about whether income, property, or sales taxes were more moral. The income tax seemed to fall fairly quickly as it was almost universally perceived as a punishment for doing well but the sales and property taxes held on for quite some time.

As I watched this circus unfold I started to think that they were basically arguing about which weapon was more moral for an armed robber to use. Is an armed robbery more moral when the mugger is armed with a gun rather than a knife? Are they more moral if they merely make you think they have a gun by sticking their hand in their pocket in an attempt to make it appear as a gun?

Personally, I can't think of a weapon that would make an armed robber more moral nor can I think of a tax that would make government expropriation more moral.