As I understand this funds didn't lent Argentina anything, they bought the bonds in the open market at a huge discount.
The hedge fund guys are just debt sharks. They're contributing nothing of value to anyone - possibly not even to themselves, because it's not so unlikely there will be international fallout that massively damages their other holdings.
Except if they didn't exist, then bonds like those sold by the Argentine government would require higher interest rates, because the original buyer would have to assume the entire risk of default, rather than having the option to transfer part of that risk in the future. That'd be bad for national governments trying to raise funds at low cost.
The point remains - giving vulture speculators the ability to hold entire populations hostage is political special pleading, not sound growth-based economics.