Why is this needed? Wasn't the move to only install local extensions by dragging and dropping on the extensions tab enough to prevent the vast majority of "installing infected extensions by mistake"? What security advantage does having to check a box for Developer Mode on the extension page offer over how it's done now, other than making it slightly harder and more confusing for the user himself to install local extensions?

Google is just one step away from making me quit using Chrome. If they ban external extensions for good with a future Chrome release, that's it, I'm done. I'll start using either Firefox or Opera, and then convince everyone I know to use them, too, just like I did before with Chrome.