Wow, some people need a good dose of reality.
Let's see:
Slavery is where you physically belong to another person, and that other person can force you to do whatever he wants. You have no free will, no freedom to do anything your master does not want you to do, and can be treated as horribly as your master deems necessary. You can never leave unless your master lets you go.
The progressive income tax is where the government takes a minority of your income and uses it to provide you with public goods that could not be provided as effectively if left up to a private company, like national defense. You still retain a majority of your income and can use it however you please. The government cannot take as much as it pleases, it can only take a set amount. Additionally, you are more than welcome to leave the country to one with less tax if you so desire. Beyond taking a portion of your income, the progressive income tax does not restrict your life in any way.
GEE WOW I DUNNO, I THINK THE TAX IS A LOT WORSE
In some countries it was the majority of their income.
But that doesnt matter. In the medieval times, the serfs had to give the lord of the manor only a third of their income. And yet they were serbs. What does that make of us?