I think it depends on the situation.
If it is down to the bank's system that no customer has any say over, or if it something that could only be avoided by unreasonable action such as not trusting my bank, or performing excessive scrutiny, then the bank should cover for their system. They insist on their flawed system after all.
However if the situation is regarding the customer doing something utterly stupid, then the bank has less of a responsibility. (Although even then they could insure against it. After all they are the ones making fortunes out of supplying a gradually less decent service.)
The one thing I'm not decided about is when the person suffering from fraud can be classed as someone who should not be expected to be vigilant. For example, it's easier to fool older folk whose minds are not as sharp as they were when younger, but the system they have to cope with is the same as the rest of us. They have no choice, the bank is dictating the situation again.
I think every incident needs to be judged on it's merits, or whatever.