I've been thinking about this issue a lot. This may sound crazy, but I think backing certain posters, aside from the preservation aspect, can compliment the look of the poster. For instance, for some artwork that has a grainy, rugged or textured look to it, backing the poster can boost that effect.
One example that comes to mind is The Outlaw Josey Wales. That is about as rugged as a movie poster can be both in subject matter and design. I have this very poster on linen with just the folds touched up. The grain of the starch and the texture of the linen boosts the overall look and feel of the poster. Josey Wales is also one of those posters that you'll likely never find rolled and looks way better with the folds touched up, while the art still allows for hiding of the restoration lines-unlike a solid black poster like Halloween, which I have but will never put on linen.
Another example of a poster that may look better on linen is Mad Max. That poster also has a very rugged, stylized feel to it and the artwork allows for easy restoration hiding. Just some thoughts. Yes, this also means I'm not boycotting all linen, just most of it!