I agree with WWW's first paragraph. A lot of the time, the general public are blamed for borrowing too much, which is strictly true but it suggests that there is a money pot from which the general public have free reign and can take as and when they please!
In fact, the bank with the financial knowledge gave them the option to borrow that amount. I'm sure the bank manager or mortgage / long term liability advisor would not be giving those loans out without consideration from the bank's risk assessment team, therefore, it has been decided by those that run the bank and assess the risk, that the general public can have those loans despite the risk that this will carry in the event of a downturn, therefore, to me, they are primarily responsible! They knew the risks but dished out the credit anyway. Of course, the poor punter that signed on the dotted line to say "I understand the above" clearly didn't have those risks conveyed to them!
In short, it doesn't seem unreasonable to suggest that the banks put a sniff of financial return above the welfare and ethical aspect of lending to those that in all honesty, couldn't afford it.
It's like a dietician giving a child a lot of sweets and then blaming the child when their teeth rot...