I'm not saying that there's anything wrong with JavaScript, but I'm just curious as to why you want it to be the only language on the server and the client. What do you see as its advantages over (Python|Ruby|PHP|Java|etc.)? Why would you want to tie yourself to a single language when you could have your choice of languages?
To be completely honest, Server Side JS or ServerJS has been growing a huge following of interested parties doing some amazing things with JavaScript (Narwhal http://narwhaljs.org/ , ServerJS https://wiki.mozilla.org/ServerJS , NodeJS http://tinyclouds.org/node/ ). The sheer fact that you openly admit that you haven't even tried the product screams "troll" and the whole "extremely slow" without any base or founding is completely ridiculous. Maybe you should take a look at the product and movement before flaming it.
imho, they need to showcase a "wow" demo app, in the same way django featured ljworld or rails had the web app done in 5 minutes