Slavery exists today, even in the US. Sometimes in the way you think about it, but mostly in a new form. By the hour.
You contract away your right to freedom while you are working. But the difference is that you can walk away at any time if you wish. That of course is assuming you're not eye deep into debt to start with.
Debt is a form of slavery. Most Americans live paycheck to paycheck. If even one check is missed they might lose everything. These people do not own anything of value. The house is rented from a stranger, the car is owned by the bank and the TV is owned by the credit card company. These people must go to work every day and work long hours just to pay back these various companies.
While there is nothing wrong with a person signing away their freedom, there is a problem with a little thing called fraud. Most contracts that a person signs are exactly that. Read my article on contracts for more information on that subject.