Do if we let them default and the lenders lose their shirts, this is a good lesson for both. Lenders learn to not make bad loans and governments learn fiscal responsibility. Most people in the U.S. More or less think it was a mistake to bail out so many big banks (decrying the too big to fail rationale) why do we have a different opinion when it comes to Greece and German banks? Let them lose the shirts.
In the end, I think Greece will blink, they'll try to work something out, but pretend they had the best of the EU negotiators. My gut feeling is that if it came down to it, Germany would let them leave the EU. I think psychologically they have written them down and if a deal happens, well, the better.
Suggesting that Greece as a whole is single-handedly responsible for this mess is silly. Yes, of course their governments over the past decade and a half were incompetent and corrupt, but it was because of the cheap loans that they could cover up the problems and keep up the appearance to the voters that all was fine. Without that, they'd have been voted out of office that much sooner. Instead, the easy money left the bad situation to fester for far too long.