For Bitcoins to be successful, it has to be able to replace the existing debt!

Whos debt? This reveals a thinking stuck in old system.

Should it replace, US debt? The Zimbabwe debt? whole worlds debt?
All money in the world, including chinese Yen or just the dollar?

Short answer is ofcourse: No.

There is really allready countries which has dual currency systems which works absolutely perfect.
In fact a dual currency system often works better.

Bernard Lietaer: Money diversity
http://www.youtube.com/watch?v=T9EI2PrDpmw&feature=related

It does not have to replace anything to be useful.
A glass can exist and be useful without having to replace all the old glasses.

I can get BTC10 that was not created out of debt, by selling something for them, doing some work, mining them, trading them
for debt based money.

I can trade a sock for 0.1Btc if I want. Without caring how many dollars a Bitcoin is worth.

When I have those. No need to use debt based money anymore.
(Except to pay taxes.)

Its not hard.

And Bitcoin does not belong to a single country.
Its independent.