There is a risk in using a bank. The risk should be low and it's normal to assume your money is safe in the bank. This incident proves it's not. The tax payer didn't take on this risk so why should they have to cover the losses?
Cocaine, mostly :P
Sounds like YC should invest more in mentoring their portfolio companies to manage their treasury correctly.
(And obviously actual losses are gonna be like 20% here, not 100%, but you get the picture).