The Greeks should have left the euro in 2012 in a controlled and dignified manner. (Actually, they should never have been allowed to join it and further actually the euro should never have been established in its current form at all, but they are both different arguments).
Greece was given too many euros for its Drachmas, was encouraged to accumulate debt in a currency it could not afford to use and was denied the traditional cure for debt of devaluation. Now it cannot afford the repayments. That's the story for many of the euro participants and it will only get worse, not better. This is because the euro is fundamentaly flawed in that it is a currency used by a collection of individual nation states each with their own problems and own priorities. The ECB is not a "lender of last resort" (because the Germans won't hear of it) so it will continue to stumble from crisis to crisis.
Of course most Greeks want to remain in the EU and the euro. I'd love a joint bank account with Bill Gates.