This article and this one argue that subprime mortgages were not the primary cause of the bursting of the housing bubble. The Wikipedia article on the Great Recession sums up the argument:

Wealthy and middle-class house flippers with mid-to-good credit scores created a speculative bubble in house prices, and then wrecked local housing markets and financial institutions after they defaulted on their debt en masse...Narrative #5 challenges the popular claim (narrative #4) that subprime borrowers with shoddy credit caused the crisis by buying homes they couldn't afford. This narrative is supported by new research showing that the biggest growth of mortgage debt during the U.S. housing boom came from those with good credit scores in the middle and top of the credit score distribution—and that these borrowers accounted for a disproportionate share of defaults.

My questions are - is this interpretation accurate, and if so, how can we prevent the same thing from happening again?