Here is the sense of the article: do not blame Wall Street, they were just responsible to make the thing collapse with shoddy financial tools! It is like saying: the food processing was pretty good (an safe) but for the fact the ingredients were rotten and poisonous:
If you wish to blame Wall Street, here’s where that comes in, but it isn’t what you think. Yes, they invented some really clever and complex financial tools to provide capital to the housing market. These were actually pretty good financial structures but for the fact that the whole enterprise was built on a house of sand and the system wasn’t set up for the collapse of the housing market.
via Message To Guevaristas Occupying Wall St. | The Daily Capitalist.