jpmorgan warnns about anz first wave, page-10

This is exactly why you can buy ANZ for $19 instead of $31.
At least you are being partially compensated for the risk.
Generally its been much healthier for investors to buy in gloom scenarios than boom scenarios.
And to further hedge your risk, buy in smaller lots over time. You may pay increased transation costs, but dollar averaging does wonders in reducing risk.

Further as a small shareholder what real chance do we have of knowing all the intricicies of bank mechanisms. Therefore create insurance for yourself by buying all 4 banks and limiting total exposure to banks as a % of your portfolio.