Mortgages (or any loan really) implies risk. This is part of why the loan is profitable: repayment isn't guaranteed. It is the bank's job to protect itself from risk. That is why it takes collateral and assesses that collateral. It's why the bank requires a down payment, especially if the borrower is on the edge of what they can afford. If the buyer defaults, the bank takes the collateral back and it's their job to make sure they are in an ok place afterwards.
So yeah, when the entire industry comes to the government and says "unless you bail us out right now our entire industry will collapse, but you're definitely going to save us because we're too big to fail," then yes, it means it's their fault. The public may have been complicit, but it's not the public's job to keep the financial industry healthy when the profits from that industry are kept privately.