So how does this allow a real panic sell to happen? You are talking about stopping the market so DDOS is unprofitable yet there are many ways to do that with out a ruleset to halt trading. Again this going to kill traders like me, who use a bot. I make most of my gains when a panic sell happens. So right there your stopping the free market, and making your exchange "normal" yet this is so young that you can't possible know what the normal price of bitcoin should be.
I'm going to bed soon so I'm only going to quote this part since it's the only relevant part anyways.
The point is to cut off a panic sell before it does long term damage. A temporary halt to trading and a gradual return to normal after a dramatic drop in price would give an exchange a chance to catch it's breath and allow cooler heads to prevail. Bot trading can still be profitable. If the price is heading south, it's heading south, nothing about a circuit breaker would stop that, it would just slow it down a bit and give people a chance to decide whether or not it is actually going down or just a hiccup.
You are a short trader gweedo and while there is nothing wrong with that, there is something wrong with people forcing the price down by lying about it. That can be a rumor that is spread, or a DDOS attack or anything else that looks like the value of the currency is about to be undermined.
If the market drops because people genuinely don't want their bitcoins anymore then that's the way the market is headed. But is it really fair that those of us who use bitcoins for daily commerce must run a significant risk of losing 50% on the value of our holdings just because the market was artificially being forced down?
Here is the scenario I'm talking about...
Joe's surfboard shop in La Playa, sells surfboards for $100. He allows his customers to come in and purchase with bitcoins. At $100 per bitcoin that means he only needs to charge 1BTC to his customer. But Joe has to buy materials and his materials cost him USD. Therefore he's setup with a sweep account. As soon as the customer's transaction is confirmed, it is swept from BTC to USD. That sweep can take a period of 15 minutes to an hour depending on how many confirmations are needed.
During this time Gweedo and company (nothing personal here, but this is exactly what you are condoning so we may as well put your face to it.) decide it would be a good idea to drive the price of bitcoins down by spreading a rumor that the exchange is about to go bankrupt, "Hey look guys, the exchange is offline, better sell quick as soon as it's up!".
This causes a run on the bank and everyone tries to dump their bitcoins at market value. This drives bitcoins down to $50 in the space of 30 minutes. Gweedo knows that the value seems to be trending at $100, so he and his friends start buying up bitcoins in hopes that in a week or so the price will recover and they can sell when the price tops out again.
This means that Joe has now lost 50% on the sale of his surfboard in the space of that same hour. If the price had moved between 90 & 110 Joe would have been fine, but at this point he is now forced to either hold onto his bitcoins and hope the price will rise. Or sell for what he can get and just eat the loss. Because he has to pay rent and his suppliers and none of them actually accept bitcoin directly, he is forced to sell and take a loss.
Now Gweedo, your opinion is that this is just fine. Joe can take the loss so you can make a profit. After all, Joe knew the risks and accepted them. Joe is just a sucker, as long as Gweedo and his bot make a profit, all is good.
However Joe is not forced to accept bitcoins. He does so as a convenience to his customers. His acceptance of bitcoins and the acceptance of thousands of other merchants just like him, helps strengthen the price of bitcoins for everyone including you. That acceptance is predicated on the premise that the price of those bitcoins will remain stable long enough for him to get into and out of his position. If the price can crash 50% in an hour then that will cause him to lose confidence in the currency. When people lose confidence in the currency they stop accepting it and if they stop accepting it then the price is driven down further, but this time it won't recover.
Therefore Joe needs to use an exchange with a circuit breaker, or some other mechanism that can allow him to get into and out of his position without suffering a significant loss in the middle. Gweedo on the other hand needs to use an exchange that is susceptible to wild pricing fluctuations so he can make a profit when people are fooled into believing that bitcoins are suddenly worth nothing.
The value of any currency is really just a reflection of the level of confidence that people have in that currency.