Its NOT conflict of interest to sell crap you bet against
During a deposition or whatever with some white old dude (I'm guessing congress, I'm not American so I don't know), Lloyd Blankfein is asked:
"Is it not a conflict, when you SELL something, and then are determined to bet against that very same thing"
And Lloyd replies "In the context of marketmaking, that is not a conflict"
And I believe he's right. Lets say you own a stock exchange, and have a special department of the company that trades stock. You have a company called "Boiled Coke" listed on the exchange, and your employee says "omg no one would buy boiled coke it tastes horrible, lets short it (bet against the stock). When you do this, you keep the company listed on the exchange in case other people wants to bet against it or invest in it.
Now, would you say this is immoral? I'd say no!
Goldman Sachs was marketmakers, like a Dow Jones or NASDAQ.