Debt based currency is a form of slavery.
Lets pretend there is no money or currency in the world, and I've decided to create some. I produce the money, and lend it out with the expectation to have it all paid back some day, and while its being borrowed, I will tack on interest that will continually accumulate until its paid back.
Now pretend you borrowed some of this money, and your ready to pay it all back. You give me back everything you borrowed, and I have all of the original currency that was lent to you, in my possesion. Because of the accumulated interest, you still owe me and since there is no more money left to pay me with, how can you possibly pay the rest off? If you borrow more money to pay the interest, which is what continually happens with the Fed and the World Bank, that will increase the interest and put you farther into debt. Essentially once you borrow debt based currency, you are permanently in debt forever.