That's exactly it, except it's worse in that every time you run an application, you are essentially letting the code author do anything as you on your machine (

That's exactly it, except it's worse in that every time you run an application, you are essentially letting the code author do anything as you on your machine (obvious, but worth stating). The only reason this works is because we trust "people" to discover this and fix it (and it will usually have consequences for the perpetrator). I'm just not sure this model works anymore, just like we don't use telnet, rcp, and all the other things that assumed you could trust the network.