Wrong. I've used the iphone 5 brand spanking new without a screen protector and brand spanking new with a screen protector.
The screen is far brighter and the image much more vivid without a sp, true. Also, the screen actuates without actually being touched sans sp. In fact, you can actually use the screen controls if your fingers hover just slightly above the screen or make the slightest contact. Freaky.
With a sp, you do actually need to touch and press very lightly against the sp to actuate onscreen controls.
Therefore, without a sp, the screen is far more responsive, responding even to the hovering of your fingers much less to it's touch.
However, I grew accustomed to actually touching the sp in order to actuate controls. I also didn't like using a bare and clean screen after using a sp. The sp accumulates some oils from your hands and fingers after a bit of use. This actually will make it easier to swipe and glide your fingers across the screen.
With a clean, bare screen, your fingers will actually catch on the glass if you press against the screen, in the same way that a squeegee will squeak as it encounters resistance as you wipe a window down.
But neither experience is necessarily better than the other; they are simply different ways of interacting with the touch screen. The reduction in screen brightness imo is more than offset by the reassurance of having full screen protection for the glass.
I don't like them myself as every one of them, no matter how high the quality, won't be as nice to touch and swipe continually. Simply put, the experience is diminished.
The iPhone 5's glass is definitely the toughest yet and after months of use mine only has two micro scratches in it (only visible in strong light).