Tax is taking money by threat of force. If this seems like exaggeration, consider the following example.

Someone lets you know that they expect you to give them a certain amount of money. If you ignore them, they send you a polite (but firm) letter reminding you of the fact. If you ignore the letter they send someone around to your home or business with a gun, to take your belongings away. If you resist they lock you up. If you resist that, they shoot you dead.

If the organization behind this called themselves 'Mafia' it would be threat of force - even if you paid before receiving the letter. It is no less force because the organization is called 'government'.

Just because the majority of people pay tax without the force being realized does not mean that it is given voluntarily, or that taking it is moral.

While it would be easy to brand all taxation as immoral, the reality is that making taxes optional would result in a tragedy of the commons, there would be no mechanism for preventing people initiating force against others, and the result would be mass slavery. The neighbouring dictatorship would invade and enslave the entire population - involving considerably greater violation than a moderate tax imposition.

This is not to say that taxes, when taken in moderation and spent on the prevention of personal violation, theft and slavery are morally right - they are just a pragmatic lesser of multiple evils.

However, taxes, when used for wealth redistribution, vote buying, pork barrelling and social control are not a lesser of evils. They are just morally wrong.