Can repeatedly touching the screen of a Macbook Air damage it? I have a 2011 MacBook Air. Are there technical/physical reasons why it might be harmful to have the screen repeatedly touched or pressed? Why or why not?
Touching your screen shouldn't do any permanent damage (unless you scratch the screen with a nail) any smudges can be wiped off with a microfibre cloth.

Using a shirt or tie to clean your screen however can damage it, so always use a glasses cloth or microfibre cloth to clean it.