I don't think the people arguing with Justin in that thread are novices or naive users, but they do seem to be unaware that when you lend your computer to someone, you should set them up with their own user account if you don't want them surfing through your stuff.

It's funny how the tech community browbeat Microsoft for years about how Windows should have been designed as a multiuser system like Unix, and then when Microsoft finally took their advice and made the necessary user-level security improvements, their efforts were ignored.