Note. That's a technical default or externally-led debt restructuring. It is not within full control of the Greek state as it would be under its own currency.
For example, a price for remaining within the Eurozone was for ensuring none of the ECB's large Greek bond holdings (approx. EUR 50bn), now or in future, will be exposed to enforced losses. This has always been politically understood.
The former. There was no mechanism to allow someone to leave the Euro - it just was never an option and the "coherence" of the system depends on this not happening. So, once you permit a member to do so, the whole Euro system becomes precarious, to say the least.
The drive for greater fiscal union, a common regulatory authority, etc, that we see now is an attempt to fix such issues - ie having so much control that these defaults never happen.
Please excuse me while I try to suppress my cynicism.
"The former. There was no mechanism to allow someone to leave the Euro"
Hmm...this is once again conflating defaulting with leaving the Euro. From the article you cited:
"Actually, a second [default], as Greece technically defaulted on its debts when it renegotiated a 50% write-off of its debts with its creditors earlier this year."
So Greece has defaulted, but they haven't left the Euro.
"The drive for greater fiscal union, a common regulatory authority, etc, that we see now is an attempt to fix such issues - ie having so much control that these defaults never happen."
I would say: "...that this sort of debt-binge on someone else's dime can't happen."
If you have a common currency, you also need these other mechanisms. It wasn't politically feasible to get this at the time, so the Euro was used as a "forcing function". Once you had the Euro, there really wasn't a way around more common financial control.
For example, a price for remaining within the Eurozone was for ensuring none of the ECB's large Greek bond holdings (approx. EUR 50bn), now or in future, will be exposed to enforced losses. This has always been politically understood.