I'm not sure I'm parsing your post correctly, but as I understand it you're talking about third party websites accepting responsibility to protect you over an insecure network connection. If that's the case, then I think you're mistaken.
Certainly SSL is not required on every page, and MITM tools have been around for some time (including fairly friendly ones like Cain - http://www.oxid.it/). At the end of the day companies such as Facebook, Twitter et al have a moral (and in some cases legal) obligation to protect the information assets you uploaded to their systems from compromise. Likewise it is not unreasonable that you take certain steps to protect yourself.
The current version of FireSheep is a real known threat. We don't know what might be in future versions. For protecting against Session ID theft, SSL and the secure flag on cookies are the way to go. Certainly for data that doesn't need to be secure (such as static publicly available graphics), there's no need to use SSL for the majority of use cases.
The use of SSL for delivering dynamic client side code (such as HTML or Javascript) is an interesting issue, but ultimately the user has to bear some responsiblity for their own actions somewhere along the line. Not every network is insecure, not every browser has to support a zillion and one insecure means of using Javascript.
Rather than using SSL on every page and expecting the web sites to do the heavy lifting, consider not using insecure bearer networks, or some sort of means of securing insecure Internet links such as a VPN or SSH tunnel.