I think you are misleading yourself @hr1. Money is just an IOU.

That's the way BitShares works :

• When you go to a bank for a loan to buy a house. The bank creates new dollars from really nothing backed by your collateralized promise to pay back the loan. In this case, your house is the collateral. The bank may call your loan and foreclose if you stop making the required payments or if the value of your house falls too much. That's how the economy works...

• In BitShares ecosystem, SmartCoins implement this concept of a collateralized loan and offer it on the blockchain. That's not misleading. It's the reality. The only difference here is that BTS is your collaterized promise to pay back the loan you made in bitUSD. And more importantly : you don't pay interest.

The two mechanisms of creating price stable currencies and creating loans are intrinsically linked.

By definition, to collateralise is to secure (a loan) with collateral

Concerning "borrow"

all you can do on bitshares is to borrow the bitusd from yourself in exchange for the BTS you already own

That's not a exchange or a sell of BTS. You just have to collateralise your loan with BTS from your wallet to create bitUSD. That's how it works. Then you are free to use your fresh bitUSD as you want. If you want to cashout, you are free to cashout. If you want to buy more BTS during a bullish period, as long as you are aware of the risks of margin call, you can. Of course, you will have to pay back the loan you made in bitUSD in bitUSD.

Dan Larimer created BitShares for helping us gaining freedom from banks. Profit it and spread the word.