A decentralized exchange is a good idea. The methods we currently have implemented are not. There have to be ways to independently verify the occurrence of an exchange, similar to how miners verify transactions through mining. If we can get something like that working (but it moves quite quickly), then we might see something of value come out of this idea, but there are still some things that have to be worked out. Not all of it is good enough yet for it to be implemented.
The concept of a decentralized exchange is good, but the first one to get high volume will become the target of the same hackers that go after centralized exchanges. Any bugs in the code will be exploited, and there will probably be bugs at first. I suspect the first decentralized exchange to get high volume will get hacked, just like the decentralized exchanges do. Making it decentralized doesn't make it invulnerable to hacks.
I cant be hacked, the money is stored on your PC, and the hacker to go after 1 person is stupid. The risk is distributed, there is no central wallet to steal from.
That is the point, the bugs will only do minor damage in my opinion, and can be quickly corrected.
The money is stored on your PC when you aren't trading, but after you start trading it would be under the control of whatever code the decentralized exchange runs on. A hacker who found a bug in that code could make a bot to exploit it through thousands of different trades simultaneously. Anyone trading at that time could have their Bitcoins stolen.