Because it doesn't seem as if you have much relevant experience, frankly. The degree to which you oppose moderately wide tires makes it seem as if you've only experienced plodding down the road on knobbies that you could hear buzzing from a hundred yards away while mostly upright on an MTB. On a drop bar bike (taking air resistance out of the equation to about the same extent as a skinny tire roady), it's really not a terribly significant difference in effort, if at all.