Alan Greenspan perfected the art of bubble creation. Real estate followed the dot.com crash as the perfect milieu for this.
Fed money was created in truckloads and hauled over to the mortgage banks, who then handed it out to anyone who could fog a mirror.
The banks knew full well that most of these loans were toxic, so they bundled them together into derivatives packages and sold them, as AAA rated investments, to foreign sovereign funds, large retirement and pension funds and other banks. The mortgage lenders and hedge funds made out like bandits ... until the music stopped.
The wishful thinking was that housing values would climb forever. As soon as the overbuilt housing market cooled a bit, and there was no more equity growth in the overvalued homes that had served as ATMs for the shakier credit mortgage holders, the monthly payments began to default... growth in the sector halted and the bubble popped.
When the buyers of the worthless derivatives instruments, who had hedged their investments with big insurers like AIG, arrived with their hands out, AIG had no reserves to pay all of the claims.
The dominoes toppled. Pension funds were wiped out. The "too big to fail" criminal enterprises called investment banks were saved - the taxpayers took one to the head for the good of the team, and the banks began looking for the next bubble to inflate.
Walking away from an upside down mortgage in this scenario, i.e. "strategic default", makes sense.
Your taxes, and those of future generations, will pay for the banker's folly. Welcome to the brave new world, comrade consumer. Of course it will all collapse soon... just as planned.