The problem is that sovereign nations don't have clear bankrupt procedure and these hedge funds are holding country as hostage for their past mistakes despite the fact that majority of borrowers accepted debt restructuring that was arranged and accepted haircuts.
If the debt and its interest grows past what country gdp can ever grow, they can never pay back and they either became debt slaves forever or keep defaulting. This is attempt at debt slavery in national level. (if person can't pay his debt ever, should he and his family lineage be responsible for that debt forever?)
I think it's reasonable to expect that in these cases banks should accept haircuts and settle like wast majority of investors did. Upholding business deal is ethically less important than country of millions being able to continue their life. The logical cost of country not being able to pay for their dept should be higher interest rates in future, not shutting country down.