That unencrypted page warning is well-intentioned but badly implemented. The way it appears makes it absolutely certain that users will ignore it and turn it off. But there are better ways to get users to think about who can see the information they submit. For example, when you start entering information in an HTTP form (not waiting until you hit submit) a kind of Clippit could appear next to the form. While not requiring you to click 'OK' or 'Go away', it could show a smiley face with the company name from the EV certificate, or else a frowny face / question mark with a link 'who will be able to see this data?'. It wouldn't get in your way so you would not need to turn it off.
There are all sorts of other UIs that could be tried to make users perceive how safe or how dangerous it is to submit information; the important thing is to make it simple, obvious, and not meaningless technobabble that you just 'OK' without reading.