Why are you going through all this hassle when you can just use Bitstamp directly, without Ripple in the middle?
Because using BTC.Bitstamp on Ripple you can trade over a dozen different currencies both fiat (e.g. CNY) and crypto (e.gg LTC). Using BTC.Bitstamp on Bitstamp internal, you can buy XRP at inflated prices or trade USD.Bitstamp, that's it.
Nonsense. Ripple offers zero value in the payment system.
For cryptocurrency to cryptocurrency, we can already send any amount directly to anybody anywhere instantly.
For Fiat currency, even with the use of Ripple, you will still need to use the banking system to move the money to the end point. You can't magically move US$100K from one place to another. Someone will still need to absorb the banking fee for the transfer.
So why even create a complex system when it doesn't improve things at all?
Please send LTC using BTC (it would even theoretically possible!)...
With Ripple you can choose which part of the banking system (if at all) and which interface you want to use. You pay fees only for clearing balances - if you needed to pay banking transaction fees (or Bitcoin transaction fees for that matter) for every single trade on Bitstamp or MtGox, you'd not trade much any more.
Bitcoins (mostly) don't get traded on-chain for cash - they are traded BTC IOU for USD IOU. Currently the issuers of these IOUs must be the same (you can't trade on MtGox with your Bitstamp balance), with Ripple they only need a market path between them and can be different.
Why does Ripple force me to manually reduce my trust with Bitstamp to zero after a transaction. Why isn't this automatic?
Because it does not really make sense in my opinion to change your opinion about believing that you could redeem e.g. BTC issued by Bitstamp just based on the fact that you received some.
Anyways, for something like this there are 3 possibilities:
Integrate it in the client which would then watch out for a certain trust line and address, once something is received there from this address - e.g. Bitstamp's hot wallet - sign and send a trust changing transaction. This means you need to be online when receiving funds and also means that you need to be able to ensure that you receive funds in one single payment (e.g. Bitstamp could send you 100 single USD for whatever reason).
or
Integrate it as flag or other server/protocol side measure. This would be probably the better long-term choice, might need some convincing to get someone at RippleLabs to write the code for you though or to get your own code for this pulled. I've heard about this idea (nulling trust lines after the first incoming transaction to ensure you only receive 1 single payment - could be made more generic by allowing time frames or numbers of transactions) already 2 or 3 times, so if you really implement it well, it might even get pulled even though they disagree with the general idea because it is a valid use case after all.
or
Wait for contracts to be done and hope that this can be encoded in there (it most likely can, requesting this feature might likely get the response "possible with contracts").