No defaulting and instead trying to rough it out and pay off a crippling debt is massively more harmful for a country. Because they have to basically cut all services and investments into the economy, which causes GDP to contract heavily, which causes a huge decrease in taxes, which causes yet more cuts in government investment.

You get a Greece like deflationary spiral that basically totally destroys your economy, and any hope you ever had of paying off the debt.

Bring on the defaults.