I don't disagree, but if you run a site of any size you will quickly realize that users will do all sorts of crazy things against the best practices for securit

I don't disagree, but if you run a site of any size you will quickly realize that users will do all sorts of crazy things against the best practices for security. One of the top (if not the top) search requests Google gets is "facebook login". What do you want to bet that a lot of those requests are coming from a shared computer?