I don't think anyone who was following what was happening doubts that home flipping played a major role in the development and ultimate collapse of the bubble. Many flippers were left holding properties they couldn't sell when the banks had scraped the bottom of the lender barrel and there was no one left to sell to. When that point was reached, the market fell faster than a bad souffle. It's not really an either/or situation. In fact, getting good data on what was really happening at the time is not easy because so much of the paper c. 2005-2007 was basically fraudulent to some degree or another.
Yet another reason we should create legislation that puts some additional brakes on buying a second house.
Makes sense to me. I certainly saw this anecdotally in LA and Miami