Generally, any time there is more demand for something the will increase. OWS entering the market for certain kinds of distressed debt would be expected to increase the price of that debt - the group of buyers in the market has increased by one, so there is more competition for the asset.
There is absolutely nothing wrong with this at all. The creditors are simply selling the debt to try and recover something from their original loan; getting more back than the would have a week ago is great. It doesn't matter to them whether the buyer is going to forgive the debt or collect it with men in leather jackets and hammers; they've sold, they've got back a few cents on the dollar and it's not their problem anymore.
How does it work? The debt is an asset belonging to the original creditor. To use the $14,000 example in David Rees's post, creditor XYZ made a loan to debtor ABC for, say, $10,000 a few years ago. They made that loan expecting to receive $14,000 back over time - that's why they did it. Now, ABC looks unable to repay the debt. The obligation still exists, but it's no longer practical or profitable for XYZ to try and recover it. XYZ has no men with hammers, no provision for accounting for irregular payments or special arrangements and no real interest in hanging on to this now-useless asset. Luckily for them, there are other companies which do want that asset, but because of the difficulties in collecting on it they're not willing to pay a lot. $500, in this case. It's worth spending $500 with the hope of collecting $14,000; if you spend $500 enough times then you'll eventually get back a few $14,000s and now you have a business. The price reflects the probability of getting that money back. In this case, very, very unlikely indeed, and if something's that cheap on Wall Street then you can be sure nobody wants it.
So that debt is bought and sold like anything else, according to the business needs of the various people involved. Your old neighbour's beaten old '68 Mustang might have been a piece of junk to him - it was too rusty to pass inspection - so he sold it for a few thousand, happy to get rid of a problem. To a specialist in vintage Fords, though, that car is worth a lot after they put the work in.
In this case there is an opportunity for a body with a bit of spare cash to benefit individual debtors by forgiving their loans, while helping creditors stay in business - and their employees feed their families - by buying their crappy assets at market rates. They are adding both charity and liquidity to a gummed-up market with very real people suffering in it.