Whose Mistake?

An odd bit from an article on the housing bust in Maricopa, AZ (via Atrios):

Many people blame the bubble and bust on investors — both amateur and professional — who speculated in new homes. "I think that was part of the mistake that the builders made, was that they allowed investors to come in and buy," Abdullah said. "Allowed them to buy tracts of homes, you know, five, six, 10 houses, and they bought them on speculation."

What's the mistake here. Builders bought a bunch of cheap land, then built houses on it, then resold the houses to speculators willing to pay a premium above construction costs despite the lack of objective supply constraints. That's a savvy business strategy, not a mistake. The people who made the mistake were the ones who bought the houses, not the ones who sold them.