I see two problems with this: causing user astonishment and taking away choice.
Astonishment: A user who resizes a window expects to see more or less content (depending on direction) as a result of this. Sites that behave as you describe are rare. This is not the behavior the user expects.
Taking away choice: users have reasons for choosing the browser settings they do, and they also have controls available. If they want to shrink the font so it all fits on-screen they can. If they need bigger fonts to see and are willing to scroll, they can do that. Your design takes away those choices, and you'll lose users for whom your design is a bad fit.
It is also not reasonable to expect users to resize their windows to fit your content. A browser window is very rarely doing one thing (tabbed browsing is the norm), and anyway it's an imposition. Don't make users work to use your site.