I think you have a strong preference in this case, and you wish to force your preference upon people in the name of the "common good." I'll let you figure out the definition of that behavior all on your own.
Instead of arguing about your clear authoritarian tendencies, here is my main reasons why I think hiding scroll bars is a good idea:
1. Information Overload: You should only show user information when they need it. Users need to know how much of the document is remaining, or where they are currently located, when they are scrolling. If they need the data, they are but a touch away from it.
2. Scroll Bars create anxiety in users who are actually reading your website. If you are under slight time pressure, as most of us are at all times, you will concentrate on your own progress through the page, rather then engaging with the content.
3. Shifting: Even on operating systems where it is the convention to always show the scroll bar, the scroll bar still disappears when there is no scrollable content. Many, websites are centered, and they have a tendency to shift the center of the website by the width of the website when the scrollbar appears and disappears. I find that behavior annoying.
4. Shifting in text boxes: when the scroll bar appears, once you typed enough text to fill the box, the text has to reflow, in order to accommodate the new scroll bar. I find this very annoying and distracting.
Finally, you keep referring to these mythical, internally confused people who keep reading only the tops of all the news articles and constantly wonder why the rest is cut off. Can you show me the following:
1. Any site that looks confusing on a mac without scroll bars. Something I can show to people and gauge their reaction.
2. Any study, article, or survey done on the subject that states that it's a severe problem. Not personal anecdotes, but actual evidence of some kind.